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Tanjiro felt it the moment Muzan’s nails pierced his chest. He choked, coughed, and lurched forward, lifted into the air by a gaping hole in his lung. The shock keeps the worst of the pain at bay, but he can’t breathe. He’s suffocating, gagging on blood. He drops his sword on instinct to claw at the wrist protruding from him to no avail, only earning a raised eyebrow from Muzan Kibutsuji instead. He can hear his friends’ voices in the distance as though through underwater. They’re calling out to him, screaming, crying. Muzan doesn’t flinch. Tanjiro can’t focus on anything other than the pain and the resounding da-dum of his own heartbeat, over and over again. It’s erratic. He can’t breathe.

Then Muzan’s eyes widen with wild glee, and his hand clenches. Tanjiro gasps. His back arches in pain as a gallon of demonic blood floods his veins, pulsing, beating, choking.

He falls to the ground. His vision clouds red. Giyu falls next. Then Kanao, Inosuke. Zenitsu. Sanemi, Kanroji, Iguro, Himejima. Dead, dead, dead. There’s so much blood. Why does it smell so good? Why does he feel so hungry? His body is shaking, trembling, aching down to his bones, but Muzan approaches him calmly. He reaches for his sword only to have it kicked out of reach. Muzan bends at the waist before him, unsmiling.

“So you’re still alive?”

Tanjiro chokes a reply that comes out like a snarl.

Huh? What’s wrong with his voice?

“Well, no matter. I guess I’ll just pump you full of my blood until you break.”

This time, when the hand comes, Tanjiro screams. The world goes dark, twisted and warped into something unrecognizable. Muzan's expression shifts to surprised, then anger, and he wrenches his hand free from Tanjiro's chest but not in time to avoid the kaleidoscope that forms around him, dragging them back, away, far, far away from any demons and humans and time itself.

Tanjiro wakes in a large, grassy field. The sky is full of stars, brighter than he has ever seen. The air smells cleaner here. A body, unrecognizable and gruesome, lies beside him. Muzan. Twisted, warped by being thrown through space-time by an amateur with no awareness of his newfound power and could barely keep himself intact. Muzan, killed at Tanjiro’s hand.

“Careful,” an amused, low voice warns. “It’s not safe here.”

Tanjiro’s body twitches, but he can’t move. He’s exhausted. He’s starving, but there’s not a single human to eat. Huh? What is he talking about? He’s not a demon. Is he?

“Oh?” Muzan Kibutsuji greets, leaning over him to block out the stars. He grins, a cruel, wicked smile, and asks, “What have we here?”

Tanjiro is going to kill him. His anger floods his veins like fire, screaming at him to get up, to rip this wicked man apart piece by piece. He struggles, fighting every muscle in his body until he wills them to let him stand. He’s unbalanced, but he can’t see past the scarlet haze in front of his eyes. He has to kill Muzan.

“Now, time travel. That’s an interesting ability.”

Muzan crosses the distance between them in an instant, landing in front of Tanjiro with that wicked smile only inches away from his face. Tanjiro reels back and stumbles. He falls to his one knee, glaring up at Muzan with the hatred of a thousand burning suns.

How did they get here? Where did the battlefield go? Why is Muzan dressed differently, and why is the wound in his chest healed?

What does he mean, time travel?

To his horror, Muzan kneels before him and tilts his chin up lightly.

“A strong demon, hm? High concentration of my blood, I see. No wonder you're in such bad shape,” Muzan murmurs, staring into his eyes with that sick smile. “What is your name?”

A name comes unbidden and unfamiliar from his lips.

“Shion…”

"Shion," Muzan repeats softly. "Won't you come with me?"

Muzan thinks he's a loyal demon. He thinks his future self hadn't meant to kill him with his power, and that Tanjiro―Shion, if that really is his name―was loyal to him. He thinks the demon slayer turned demon is on his side.

At the moment, Tanjiro doesn't stand a chance of defeating this Muzan. He's weaponless, weak, alone, and if what Muzan says is true, lost in the past. His only chance is to play the role and bide his time until the old—new pillars return, until they can fight together again. So, he allows Muzan Kibutsuji to help him to his feet and move them into the shadows of the forest as the sun begins to break the horizon. They make it to an ancient house in the mountains to rest.

After given a bath and a pair of clothes to change out of his torn and tattered robes, Tanjiro—Shion—lays his head down to rest for a long, long time.

~+~+~+~

The quiet is the first thing he notices. The air is still and cool, permeated by the sweet scent of flowers. He sits up slowly, feeling the ache of a body long-rested. The hunger is gone. The hatred, too, replaced by a tranquil sensation of warmth. His hair is long and messy, tied back with a leather cord. He looks around calmly.

The room he's in stretches on endlessly with layers upon layers of rice paper doors and tatami rooms, winding walkways and dizzying heights. He sits upon a table, laid out like a doll with a needle in his arm attached to a blood transfusion. His veins pulse and throb around the needle and he pulls it out gingerly, wincing as its removal sends a jolt of white-hot pain through his arm.

He steps off the table and takes another look around at the apparatuses and notebooks laid out, detailing tests and experiments on him. Muzan has been studying his blood, hoping Shion might be a new breed of demon sent back in time by his future self as a message, a key. For that reason alone he has let Shion live and saved him from the sunlight in that field.

He feels like he's going to be sick.

"Ah, you're awake."

Shion turns. Muzan stands behind him where he most certainly wasn't a moment ago, a smile on his face. His hands are clasped behind his back and his red eyes burn with concealed anger.

"I've found a palace for you to make your own," Muzan announces in that same calm tone of voice with an undertone of pure fury. "It is currently occupied by demon hunters, but that shouldn't be a problem for you. Right?"

His smile sharpens, giving the idea Shion doesn't have a choice.

"No, My Lord."

He bows low.

Muzan's grin widens, and he murmurs, "Good."

Shion is definitely going to be sick.

~+~+~+~

The castle is beautiful. It rests high above the surrounding farmland and village upon a hill, surrounded by high stone walls topped by white tiles. It rests against a river, with lush trees backing the castle.

Shion stares up at it from the opposite bank before he decides to walk right through the front door.

The negative effects of Muzan's blood have mostly faded, leaving him stronger than he ever was as a human. His speed and agility as a demon surpass even that of the Breath of the Fire God. He can imagine, if he were to combine them, he might be stronger than an upper moon.

He scales the outer wall and lands crouched in the empty, moonlit courtyard. He looks up. A startled guard meets his gaze with his hand on his blade, but Shion kneels before him.

"I come bearing no ill will," Shion swears calmly. "I ask only for a place to stay. I am strong, I can protect your master better than any human at night. So please, I beg of you."

He presses his hands to the ground and bows low, prostrating himself before the samurai.

His scent is strong. Human, blood, food, but Shion doesn't allow himself to move. He was a demon slayer. He will not falter. He will not fail.

After a long moment, the sound of a blade being drawn meets Tanjiro's ears. Footsteps draw closer and he closes his eyes, preparing for the swing. If this sword is not a nichirin blade, he will be fine. If it is, well… He'll just have to hope it isn't.

"Tenzen," a deep, commanding voice echoes. "What is the meaning of this?"

"A thief, Lord Shidou."

"Oh? And what has he come to steal?" The lord of the castle stares down at them over the balcony as he continues, "He looks well-dressed and clean. If he is indeed a thief, he must have come for nothing short of a woman's heart."

Shion holds back a snort and earns a glare from the soldier. The daimyo smiles.

"Raise your head, thief. What is your purpose in trespassing on my property this fine evening?"

Shion looks up, but remains kneeling. The daimyo has long hair that falls down his back, layered with grey strands. His expression is kind, although his features are sharp and severe.

"I humbly beg your hospitality, My Lord," Shion calls out. "I have come to serve you. All I ask for in return is a place to stay."

"Can you fight?" Lord Shidou asks calmly.

"Yes, My Lord."

"Prove it."

Shion frowns. "Excuse me?"

Shidou nods to the soldier and says, "Get the man a sword and wake the others. I want to see him fight."

"Sir!" the samurai shouts with a bow.

He runs off. Shion and the daimyo stare at each other, assessing, until a crowd begins to gather. Someone hands Shion a black katana with a similar weight to the one he used to wear. He holds it for a moment in its sheath, appreciating the blade and its weight.

When his opponent, Tenzen, faces him in the courtyard and readies his blade, Shion smiles. He draws the blade slowly, watching it in the light of the moon. It's full tonight, illuminating the courtyard with bright white light.

Shion hands the sheath to the soldier who lent it to him and settles into a familiar stance. His breathing is calm and steady. Once, using breathing techniques was an inhuman feat, but for many years now it has come naturally to him.

He doesn't alter it or use the Breath of the Fire God, but he still avoids each of the man's attacks and defeats him in an instant. He doesn't harm the man, only known his sword out of his hand and pins him to the ground with the tip of his borrowed blade. Tenzen looks up at him with wide eyes, and Tanjiro catches a glimpse of his reflection for the first time since he turned.

Not much has changed. His irises are still the same dark red, but his sclera have turned black. His teeth look sharper, and the scar on his forehead has darkened. His clothes, too, are different; dark robes of swirling red and purple patterns instead of his old checkered haori, and a black hakama which no longer has the Demon Slayer logo emblazoned on the back.

He turns away from the man and kneels before the daimyo, laying the sword gently on the ground.

“Excellent work, young man,” Lord Shidou comments, his voice flowing with pride. “What is your name?”

“...Shion.”

Surprise flickers across the man’s expression before his features settle into a grim frown, his hands clasped behind his back.

“Shion,” he repeats. “What is your clan name?”

“I don’t have one.”

“I see,” Shidou murmurs, eyes darkening. “And where are you from?”

Shion looks at him calmly. His town was founded a long time in the future, here, if Muzan is to be believed. He must keep his true identity secret for now, if his plan is to succeed.

So he bows his head and says, “A place very far away.”

Shidou looks at him closely. Shion doesn’t dare to breath, his gaze fixed on the packed earth of the courtyard before him. The soldiers around him watch carefully, eyeing the way he holds himself and the silks that clothe him.

“Welcome, Shion,” Shidou announces, tilting his chin up slightly to look down at his new servant. “We will discuss the details of your employment in the morning. For now, have Tenzen show you to the northern room on the second floor. That will be your new quarters.”

Shion looks up, readying a request on his lips, but Shidou turns away and answers before he even asks.

“The sun doesn’t penetrate there.”

Shion is left to follow Tenzen up to his new room, dazed and filled with gratitude.

Chapter Text

"Shion, right?" Tenzen asks, offering his hand to help him stand. He wears a smile when he says, "Welcome to the family, brother."

Shion looks up at him with wide eyes and takes his hand with a smile. He's taller and stronger than Tenzen, and he wonders just how much time has passed since he fell.

"Where'd you learn to fight like that?" another soldier asks, clapping his hand on Shion's shoulder as he comes up behind him, grinning. "You're one hell of a samurai!"

Shion smiles and looks around. He's taller than most of the soldiers. All of them are human with red beating hearts and gushing blood he can smell, he can hear, but he has to resist. He may be a demon now, but he must resist temptation. He can't sink his teeth into their flesh; he can't kill them.

He's a demon. He's a demon, but he must protect humans. He cannot kill them. If he has to wait a thousand years before he can kill Muzan at last, even if he has to sleep and bite his tongue to keep himself from breaking his vow to protect humans, he will not break. He cannot let Muzan win again, for a victory at the cost of so many deaths is hardly one at all.

He bites his tongue. The rancid blood of a demon fills his mouth and he uses it, as sick as it makes him feel, to keep himself sane. He remembers the faces of each of his friends, his family, falling one by one right before his eyes. He was helpless then, he's helpless now, but if everything falls just right in the future, they can win. He's sure of it. They can kill Muzan.

When Tenzen and the others pull Shion inside the castle, he focuses on the decor to distract himself from the sweet scent of human blood. The interior is beautiful, decorated with thick dark walnut planks and wooden posts. Paper lanterns illuminate paper walls with intricate, detailed paintings. The first floor is decorated with scenes of trees and an ancient garden. The second, up a flight of stairs, features waterfalls and oceans, koi ponds and lilypads.

His room is decorated with a painting of a rocky waterfall across the doors. He exchanges bows and thanks with Tenzen before the other soldiers leave him to settle in.

Muzan appears on the windowsill as soon as their footsteps disappear. His posture is calm and unthreatening, but his eyes burn with fury. Shion folds to the floor in an instant, his heart pounding in his throat.

"You took the castle," Muzan remarks with a step forward, the stench of murderous intent radiating off him like strong perfume. "You took the castle, and refused to kill a single demon slayer in it."

Shion doesn't dare look up.

Muzan falls silent. He stands over Shion, imposing and furious. Shion's mind is completely blank, devoid of everything except fear.

After a long moment, Muzan sighs. The murderous intent vanishes like it was never there, replaced with disappointment and mild curiosity. He turns away toward the window, as one hand brushes a strand of his hair out of his eyes.

"I will allow you to live despite this transgression. I'm sure my future self sent you to me for a reason, even if I haven't discovered it yet." Muzan turns to look at him over his shoulder, eyes wide and warning. "If you do not prove yourself useful in due time, I will kill you."

Shion cannot answer. Muzan disappears through the open window and Shion's body relaxes against the floor, spent.

How long can he last like this? How long can he survive without eating humans? Nezuko could do it, but was she different? Will he starve before he can stop Muzan forever?

No. He'll force himself to adapt, as painful as it might be. He will defeat Muzan once and for all, and he won’t allow his family to die again.

~+~+~+~

"Shion! Can you help me move this?"

"I need some help with the garden. Are you free on Saturday night?"

"Lord Shidou has guests arriving in twelve days, so he's increasing security. Will you be able to work guard duty?"

No matter what his brothers and sisters ask, Shion always answers, "Yes!" with a cheerful grin.

None of them mention his demonic strength or nocturnal schedule unless as a joke. Most of them know. All of them have come to see him as a member of their family, demon or not.

It gets easier to resist. Shion no longer has to bite his tongue when surrounded by humans, and he can stand the smell of blood. He takes to sleeping for exorbitant periods of time every once in a while to maintain his strength, and Muzan becomes fascinated with the shift in his blood. According to Muzan's notes, Shion's body has forced Muzan's cells within him to undergo a biogeochemical transformation in the absence of human nutrients, effectively forcing him to begin to become a demon-human hybrid. He hasn't mastered the sun yet, but Muzan suspects he could, if exposed under the right circumstances.

Aside from his body's transformation, Shion becomes useful as an informant to both the Demon Slayer Corps and Muzan.

He learns that Lord Shidou is the rock pillar, and many of his employees, his "family," are demon slayers in training. Tenzen is, too. Shion watches them all age and mature over the years. He mourns with Shidou and the rest when each batch who goes to Final Selection each year returns, dwindled to a fraction of what it was before. There is one year when only one returns. Tenzen's group had gone to Final Selection prepared to die, and Tenzen was the only one who survived. Shion was on watch duty that night, and Tenzen collapsed into his arms at the gate, sobbing.

As Lord Shidou's disciples grow and move on, Shion stays at the daimyo's side. He welcomes new trainees with his kind smile and delicious food he himself can't eat, for it makes him ill. Shion's grasp of human emotions has dwindled, but he still knows empathy. He still knows rage, and fear, and lust. He can still feel happiness and sadness, but the edge is dulled. He can no longer cry.

Lord Shidou ages and ages, but the only things about Shion that grows are his hair and his mind. Shidou falls ill after many years, and invites Shion into his room one night.

Shion kneels at his bedside with a sad, kind smile and takes the old man's hand. Shidou's vision has deteriorated over the years and he looks off into the distance over Shion's shoulder. His grip is still like iron, but Shion doesn't flinch.

"Shion," the old daimyo rasps, throat cracked and dry with age. "You have served me well."

Shion startles. It is rare for Lord Shidou to talk about his inevitable death. For him to speak so casually about it, as though his life is already over, is even stranger.

“My Lord,” Shion begins, but Shidou shakes his head.

“You should call me Father, Shion. You are the son I never had, after all.”

He blinks. All his life, Shidou has never had a successor. He never married, and his disciples have always assumed his estate would become another Wisteria House. Shion did, too.

“Father, what do you mean?”

Shidou looks through him with cloudy grey eyes. Shion stares back, grave and caught between hope and disbelief.

“I would like to entrust my estate to you, Shion.” The old man takes his hand in both of his own and squeezes tight. “I have already written it in my will, but if you do not wish for it, you may pass it on to someone else.”

Shion falls silent for a moment before he replies, soft, “I cannot accept this.”

Shidou’s expression doesn’t shift. His grip tightens, but Shion remains strong.

“Father, I… I have not been entirely honest with you,” Shion admits, head bowed. “My Lord, I am a demon. I cannot in good conscience accept the estate of the Rock Pillar.”

Shidou smiles and releases his hand.

“Bah,” he grumbles with a dismissive wave. “Thirty years ago, I invited you into my home under the cover of night because you came and bowed your head to a single, weak human armed with a sword that couldn’t kill you. For thirty years, I have watched you do nothing but protect and teach young humans, even as Muzan studied and threatened you.” As Shion’s eyes widen in surprise, the old daimyo raises his hand to silence him and continues, “Yes, I know. What kind of pillar would I be if I didn’t know the king of demons kept stealing my own son away from me?”

“I should have told you sooner,” Shion murmurs.

Shidou reaches up a shaky, frail hand to cup his cheek and tell him, “If humanity ever stood a chance of defeating that damned man, you will be vital. Don’t you ever forget that, my son.”

When the old man’s hand falls and his eyes close, Shion feels tears spill down his face for the first time in decades.

The Lord’s funeral is long. The tens of demons slayers still living out of the hundreds he trained return from their war to grieve their father, their grandfather, uncle, and master. Shion leads the procession under heavy layers of black fabric and a wide straw hat, his face concealed by a veil to protect him from the sun.

The wake is huge. The gifts brought to Shidou’s alter vary widely from flowers to expensive jewels and precious metals. His body is cremated and buried in the local cemetery under a tall stone, engraved with his name.

Then comes the matter of succession. Shidou was a powerful lord, and his land should go to someone. Those who knew him are torn in three ways: to turn the estate into a Wisteria House would be expensive, but beneficial; to pass it on to his oldest descendent, Tenzen, would be logical but against his will; to give it to the demon Shion who shares his name and cared for him to his dying breath is the most likely option, but what is the risk of granting a demon such a residence? Even when Tenzen announces he has no interest in the estate, the debate remains.

At least, until the young Ubuyashiki lord appears to read a letter sent to him by Lord Shidou in his dying days, to be read only if this situation were to arise after his death.

“My Lord,” the letter begins, “I am writing to you in regards to the matter of my estate.”

As the rock pillar, he admits his plan had been to pass his estate on to a future pillar, if possible. If not, he would have preferred it become a Wisteria House.

The audience murmurs. Ubuyashiki silences them with a hand and continues.

“However,” the letter continues, “I have had a change of heart. Thirty years ago, I took in a young demon who bowed his head to a young man with hardly any training and humbly asked for a place to stay in return for his service. With one look at him, I saw he had the power to slaughter all of us that night. Yet he chose to bow. In the thirty years he has been in my care, he has not done nothing but help any man, woman, or child who has crossed his path.”

The crowd turns to Shion’s masked form with wary, curious eyes. Shion kneels at the front of the crowd beside his brother, Tenzen, who casts a glance at him with a knowing smile. Tenzen’s face has grown as well, and his hair is beginning to turn grey. Yet, his eyes sparkle with the same kindness and love they always have toward his brother.

“And so,” the letter concludes, “I ask that my son Shion inherit not only my estate, but my title as well. Make him the Demon Pillar. He will be a valuable asset to the Demon Slayer Corps, I am sure.”

Ubuyashiki folds the letter and tucks it into the sleeve of his robes. He stands before them with a serene smile, head held high.

In a kind voice, he announces, “I leave both the former Rock Pillar’s estate and the title of the Demon Pillar to Shion, as Lord Shidou requested.”

Shion isn’t sure which he thought would be worse: outrage, or immediate acceptance. The outcome he was not prepared for was dead silence. For once, not a single demon slayer breathes.

Shion stands and turns to face the crowd. Every pair of eyes is fixed on him. The sun still shines down bright, but some cloud cover has shaded its light. He reaches up slowly to fold his veil back, and reveals himself to them in the sun.

“I understand if you do not accept this,” he tells them calmly. His voice echoes across the courtyard. “I told Lord Shidou I could not accept this gift. At the time, I did not know of his request to Lord Ubuyashiki to grant me the title of pillar, but I believe it is time I tell you all who I truly am.”

He spares a glance at Tenzen, who flashes him an encouraging smile and nods, once. Shion’s chest fills with courage and he returns to the crowd, his brothers and sisters and everything else. He looks at the children he raised and trained, at their attentive faces, and smiles.

“I remember when I was a human.”

A few faces flicker with surprise, or smile in understanding. No demon has ever remembered their life before until just before death, but then again, no demon has been as kind as Shion.

“I used to be a demon slayer too,” he admits, raising his fist to show the mark on the back of his hand that reads his rank, Hinoto. “It is true that I am a demon, but I have never eaten a human. I am going to make that man pay for every life he’s ruined, even if it costs me everything.”

Tenzen smiles. Then, slowly, he lowers his forehead to his fingertips, pressed against the ground. The sea of demon slayers trained by the former Rock Pillar and the newly christened Demon Pillar bow their heads one after the other.

Shion stares out at them with shock, his black and red eyes wide.

Tenzen breaks the silence in a voice overflowing with love.

“We will follow you to the ends of the earth, Lord Shion.”

He can’t help the smile that forms on his lips at that.

Chapter Text

For the most part, Shion is allowed to live in his castle as he pleases. Time progresses, the demon slayers kill and die as the demons do, and Shion comes to see they really aren't that different. He keeps an extensive map of what must happen within his mind, carefully planned down to who he can save and who must die as they were meant to. Among the names on the latter list are those of his own family.

His mother and father will succumb to illness. Nezuko and the children will be attacked by a demon and killed, but Nezuko, dear Nezuko will live on as a demon. Tanjiro, a name that has long become unfamiliar to Shion's ears, will save her, become a demon slayer, and lead the fight to Muzan. He's sure of it.

Until then, he must bide his time.

Eventually, Muzan carves the number "Upper Moon Zero" into Shion's amaranthine eyes. Time advances readily and the ranks of demon and human forces change, grow, and expand. Not once does a Pillar seek out Upper Moon Zero, and not once is the absence of the Tenth Pillar mentioned in the meetings. Before long, the only ones who know where to find him are the Ubuyashiki family and Muzan Kibutsuji himself.

The first man who charged the castle against the Demon Slayers' warnings was the father of a beautiful young woman who fell in love with the lord of the castle, a man of indeterminable age with sharp fangs and dark, vivid eyes of an unnatural color. The locals call him the Spirit of Himeji Castle, one who grants favors and asks nothing in return but courtesy to his other guests. The father feared this ghost seduced his daughter with the intent to kill her or keep her enslaved, and rode to the castle on horseback with the intent to free her.

When he arrived, the sun was shining bright and the sky was clear. He rode past the unguarded gates into the lush, green courtyard of the palace. He held his sword high overhead and called the Lord to give him back his daughter.

The man’s daughter came to the balcony and leaned over, dressed in fine white silks her family certainly could not afford. Her long black hair hung in sheets around her, framing her lovely, pale face. She told her father she was not being held against her will, but Lord Shion could not step into the sunlight. The man tried to convince his daughter she was being deceived but she swore Shion would never do such a thing. At length, the woman exclaimed if her father would not listen to reason, she would prove her lord’s intentions.

To her father’s horror, she stepped upon the railing and extended her hands outward, face tilted up toward the blue sky. Her yukata fluttered in the breeze, catching opalescent patterns in the light. A voice screamed from inside for her not to jump, but her body began to lean over the edge.

Just as the man’s eyes widened in horror and his daughter’s feet slipped off the rail, a clawed hand grabbed her around the waist and wrenched her back. The Lord finally revealed his face in the sunlight, grimacing in pain. He was hideously burned, but once the woman’s life was saved, it cleared. He blinked at the sky in startled delight. The woman threw her arms around his neck and sobbed with relief, but Shion was too busy staring at his unburned hands in the sunlight.

He’s waited nearly a hundred years for this.

Muzan has waited centuries.

Inside a beautiful palace with a handful of gorgeous men and women, Shion spends his days dressed in fine textiles sending aid to whoever calls for it. He organizes the demons, protects the demon slayers, and does his best to help other demons alter themselves and evolve, like him. Some of them do. Some of them die in the process, starved or burned to death in the sun.

Muzan refuses to attempt the transformation until he is sure it will work, and Shion suspects he does not trust him. Good thing, too; if Muzan were to overcome the sun, he would be undefeatable.

Not that he would ever perform the necessary sacrifice to do so.

Throughout time, the name and existence of the demon pillar has faded from the living memory of the Demon Slayer Corps. Some have held suspicions about the Lord of Himeji Castle’s humanity or lack thereof, but each time the rumors have arisen the locals assured everyone there was nothing to worry about there; the rumors have already been investigated and there is no threat to human life in the Haunted Castle of Himeji.

Which is exactly what makes Sabito suspect the spirit of the castle may be stronger than any demon they have ever encountered before.

“What do you know of Himeji Castle?”

Sabito’s question catches Giyu off guard.

They’ve been travelling west for their missions lately, crossing paths where they can. They are resting in a Wisteria House not far from Kyoto where a natural hot spring flows from the center of the earth, soaking in the bath to rest their tired limbs.

“The haunted castle to the west?” Giyu returns calmly.

Pillars do not get much rest. When Giyu was offered the title, he argued until he was blue in the face. Only then did the Master tell him Sabito was offered it first and refused in the same manner, insisting Giyu take up the mantle in his stead.

Giyu went home that night with a new rank, and was glad to see the mark on Sabito’s hand, too.

Sabito hums his assent.

“Not much,” Giyu admits. “Why are you thinking about that now?”

Sabito looks up at the stars above and asks, “Do you believe in ghosts, Yuu-chan?”

“No.”

“Exactly.” Sabito closes his eyes and leans back against the side of the bath. “Tomorrow, we leave for the castle.”

“But what about our missions?” Giyu asks, because sharing their rank means sharing responsibility, too.

“This is my mission. You will likely be asked to come along.”

“Why send two pillars after what may or may not be a demon?”

Sabito opens his eyes again and shoots him a sharp look, unsmiling. The scar on his cheek is subtle in the moonlight, but still there.

“Because,” Sabito explains lowly, “Either it isn’t, and we will both be relieved, or this is a demon who is too smart and capable to leave unfinished meals.”

Giyu’s breath catches in his throat. Sabito climbs out of the pool and wraps the towel around his waist; not that Giyu hasn’t seen him without it many times before.

“We leave after breakfast. Sleep well, Giyu.”

Sabito leaves quietly, and Giyu follows shortly after.

~+~+~+~

Giyu is indeed placed on the same mission. Whether or not Sabito had a hand in that is anyone’s guess.

They hire a farmer to drive them into town in his wagon. The trek still takes a little over a day, with rests for the horses, and they make it around noon of the following day. The castle presides over the surrounding village like a great dragon protecting its hoard, and as they step off the driver gives them a warning.

“They say the Lord of Himeji Castle is a ghost, cursed to haunt these lands until he produces an heir,” he says gravely, nodding toward the castle. He smiles at the young man standing before the gate and adds, “Between us? My sister has so far lived a long, happy life with that man. He may not be human, but I don’t think you’ll be needing those swords.”

Sabito and Giyu exchange a glance before the man rides off. They turn to the gate with their hands on the hilts of their swords, and give each other a nod.

The gate is unlocked.

Giyu steps through first, his sword partially drawn. Sabito follows, both their expressions grim.

The garden is bursting with vibrant green bushes and colorful plants. A few people stand amidst them, talking to each other or tending to the garden. They are dressed in beautiful blue and red robes with subtle patterns, yukata and hakama with low, polished geta. Some of them look up when the demon slayers enter, and a man at the far end standing just within the shadow bows his head to the woman at his side. She bows and waves for the others to follow her inside.

The man stands in front of the castle, arms folded in front of his chest. He’s dressed in fine silk hakama with golden dragon embroidery. His hands are hidden by his sleeves. His features are sharp and fine, his full lips set in a soft frown. A simple black veil conceals his eyes.

He could easily be mistaken for a human, except for the two pairs of black horns protruding from his skull.

As they draw closer, Giyu notes the man easily dwarfs them in size. He stands a full head above them, and not just because of his geta. His horns spiral into the sky, two black sets with rounded tips. One set twists straight up from the crown of his head while the other curls out from his temples like a ram.

His expression is dark and watchful, but kind. He remains completely composed even when Giyu and Sabito draw their swords and settle into fighting stances in front of him.

"I assume you have come as my executioners."

The demon's voice is kind, almost warm. He speaks with ease. Clearly, they aren’t the first to do so.

What happened to the others?

“Our mission was to uncover the identity of the Lord of Himeji Castle,” Sabito proclaims solemnly. “However, seeing as you are a demon, and a powerful one at that, it is our mission to exterminate you.”

Strangely, the demon smiles.

“Would you believe me if I said I asked Lord Kaguya to send you two?”

Giyu startles. Sabito does a better job of concealing his surprise, and grips his sword a little tighter.

“No.”

Sabito strikes first.

The sun disappears. No, that isn’t right; it turns to night. The world ripples, and the two of them find themselves standing in a huge open field under a starry night sky.

“Have you ever wondered who saved you during Final Selection?” the demon’s voice echoes through the dark, smiling.

“Where are you!” Sabito shouts, pinning his back against Giyu with their swords raised, watchful of the shadows.

“Who gives the Demon Slayer Corps tips on the location of well-hidden demons?” he continues, almost laughing.

A flash of smoke, and a voice in their ears whispers, “Me.”

They separate and whirl to face each other, only to find nothing there but a fading cloud of black smoke.

The demon’s musical laughter echoes across the field. Giyu can feel his heart pounding hard in his chest, breath coming short. This demon might be more dangerous than any they have encountered before. Is his ability to manipulate space-time? Illusory? Is that the point of his veil?

“You have no proof!” Sabito proclaims, yelling into the void.

“Ah, but I do.”

The illusion fades, and Giyu finds both himself and Sabito pinned to the ground and restrained by the humans who were previously scattered throughout the garden. The demon stands above them, grinning a sharp smile with a black clawed finger pressed to his lips.

“The man who saved you wore a violet robe with scarlet flowers, and a white demon mask,” he says softly. “He carried black sword, and shed tears for the demon he slayed. Believe me,” the demon lowers his voice, his tone turning sad as his smile falls, “I would have saved him too, had I found a way.”

Then Giyu and Sabito find themselves wrestled to their feet and marched into the castle, their swords carried in the arms of watchul humans.

“We will break the spell you have them under!” Sabito swears. “You can’t hold us forever! The Master will send more after us! He’ll defeat you!”

“Oh, my dear Sabito,” the demon purrs, reaching out one clawed finger to tilt his chin up.

Sabito flinches and jerks his chin away from the demon’s grasp.

“How do you know my—”

“That, my old friend, will have to wait for another time. Don’t worry; I don’t intend to keep you long. You have entered a place where nothing is as you know, and corpses come back to life. Do not fret, my fellow pillars. I am an enemy of that man as well.”

Before either of them can ask what he means, they are brought into a large, wooden-floor room with glass lanterns and stairs winding up to the second, third, fourth floors. Beautiful, hand-painted doors line the halls, which are made of dark, polished wood. Together, they are taken through the castle to a bath behind it, stripped of their clothes, and told to wash up. Curious, but having spend a day and a half among hay and bugs, they are grateful for the chance.

A warm bath awaits them through a wooden archway, where they soak until two young men come to bring them a change of clothes.

“What the hell?” Sabito murmurs, taking up the robes brought for him.

Giyu takes a closer look at the sapphire yukata brought for him with a frown. It’s a heavy cotton fabric with the outlines of waves carefully embroidered on it in a shining silver thread. Sabito’s is red, with a similar style of embroidery that has golden waves instead. Both have been gifted with a white obi, and fresh socks.

Why give your prisoners such nice things if you only intend to eat them?

“Don’t worry,” one of the young men says with a smile. “I can’t explain everything, but Shion-sama is a kind person. He brought you here for a reason.”

“That doesn’t necessarily make me feel better,” Giyu mutters, but when the man turns and asks them to follow him, he does.

Their swords are nowhere to be found. Giyu and Sabito are led to a large tatami room with a table set for tea. Four red cushions surround it, and the demon sits on one in soft discussion with a woman at his side.

“...And make sure Tsuki takes her medicine, she often forgets. Can you ask Take-chan and Abe to clean up the boys’ room before their stay tonight? Oh, and send word to Tamayo-san. Write, ‘The pieces are falling into place. It is nearly time.’ She will know what it means.”

“Yes, my Lord,” the woman responds with a bow.

He smiles and gives her a kiss on the forehead before she leaves, covering her blushing face behind the sleeve of her pink kimono.

The demon turns to them with a smile.

“Welcome,” he greets, gesturing to the other seats. “Please, make yourselves comfortable. You must have had a long and difficult journey to get here.”

Giyu and Sabito cannot fathom why this demon is even feigning niceties, and Giyu does not drink the tea.

“Who are you?” Sabito asks softly, kneeling across from the demon.

He smiles, and Giyu feels a shiver of recognition in it. There’s something so very kind and tragic to it. It's familiar, like déjà vu.

“My name is of little importance,” the demon claims. “I have been given many names over many years, but for now, you may call me Shion.”

That sense of familiarity tingles down Giyu's spine again, but he's never heard that name before. He's never seen this man, he's sure, so why?

One glance at Sabito assures him he's not alone. Sabito is sitting still, eyes wide. His lips are parted slightly.

Giyu's initial fear is that the tea has been poisoned.

"It was you," Sabito whispers, gaping at the demon. "Zero. I saw it through the mask, but I― How did you get past the wisteria?"

Shion inclines his head, smiling.

"There are ways for my kind to enter. The trouble was leaving, but Lord Kaguya was kind enough to part the trees for me."

"I would have died," Sabito breathes, wide-eyed. "It would have killed me."

Shion's smile disappears. He considers them with a solemn expression, and something tells Giyu this demon may be more than he claims.

"I know."

His voice is so soft and broken, so gentle it nearly brings Giyu to tears. Sabito covers his mouth with his hand to muffle a sob as tears begin to spill from his eyes, and Shion offers a piece of cloth with a sympathetic smile.

"I apologize, but the sooner we discuss our business, the better," Shion says, turning to Giyu. "Lord Kaguya has sent the two of you upon my request for a very particular reason: I believe you are the only ones willing to look beyond my race."

"You are a demon," Giyu returns. "You eat people."

"No," Shion argues, grave. "I do not."

Giyu startles.

“All those you have seen here are humans who live here of their own free will, people I look after,” Shion explains with a furrowed brow and a tilt of his head, tone making his exasperation evident. “I do not eat them, Giyu-san. Ask any of them for their word and they will swear on it."

“We still have no proof they aren’t under your control,” Giyu says, firm.

“My demon art does not give me control over people’s minds,” Shion sighs. “If it did, that man would already be dead.”

He spits the last part like a curse, and Giyu almost believes it is one.

Sabito finally recovers, and raises his head.

“Why did you bring us here?” he asks, voice soft.

Shion turns toward him with a solemn expression and says something neither of them expects.

“I need your help.”

Giyu and Sabito exchange a glance.

Shion bows his head as he begins, “Many, many years ago, I awoke in a field under the stars where I met a man who believed me a loyal servant. He had killed all I held dear before my eyes and flooded me with his blood in an attempt to kill me, yet I managed to retain my memories. I did not lose myself that day.”

Giyu finally accepts the tea. Sabito has finished half his cup, and if this demon were truly an imminent threat, he would have already killed them.

Shion’s grip tightens around his mug, sharp black nails standing out in such a human gesture.

“You don’t have to believe or trust me,” he tells them. “In fact, I would be dismayed if you did. All I ask is for you to defeat that man, and for me to be there when you do.”

“The Demon Slayer Corps have no leads on the whereabouts or appearance of Muzan,” Giyu points out. “How do you expect us to find him?”

Shion smiles, but there’s something achingingly sad to it.

“I believe Lord Kaguya has a plan for that, Giyu-san.”

Something in his voice prevents the water pillars from asking exactly what kind of plan.

The demon rises to his feet and clasps his hands behind his back, crossing to the painted doors, these with scarlet-blossoms on the gnarled branches of trees. The sun is beginning to set already, casting them in a warm glow. He bows his head toward them, unsmiling.

“I have spent nearly four hundred years gathering support and training demon slayers.”

The weight of his presence grows, heavy and swirling with hatred not for them, but for a man much older, much stronger.

“I have helped create a new race of demons who remember their lives and do not eat human flesh. I have watched every single preventable death from afar for four hundred terribly long years, I have waited for the pieces to fall in place so we may defeat that man. In all that time, I have served him.”

Shion turns toward them again and with dark hatred in his voice, swears, “I will not let it go to waste.”

Then, in a heartbeat, he disappears.

Giyu and Sabito are left kneeling beside each other in an empty room. The weight of the demon’s presence disappears with him, and the pillars finally feel safe to breathe. Sabito was right. There is no ghost who haunts Himeji Castle. It is a demon, an ancient, powerful, furious demon who will stop at nothing to avenge the lives of those he has lost.

God help any who stand in his way.

Giyu and Sabito are tended by more humans after the demon lord disappears. His “guests,” as they call themselves, answer the pillars’ questions readily in support of their lord’s story.

Some of them are training to become demon slayers, while others simply care for the palace and tend to their lord when he asks them to. They range in age from children to those nearing the ends of their lives, and they all hold reverence for him. In their eyes, there is no one kinder than Lord Shion.

They also say he spends much of his time asleep, but has been awake much more lately. He rarely leaves the palace these days, but his crow flies constantly. No, he doesn’t spend much time with humans. No, they are not the first demon slayers to visit; they are, however, the first pillars to be sent. Yes, it’s normal for him to disappear like this. They likely won’t see him again before they leave. In the meanwhile, would they like to rest here for the night? Dinner is always delicious. Oh no, Lord Shion doesn’t make it. He doesn’t seem to eat anything, really.

The conversation continues like this until Giyu and Sabito are led to their room by the young woman who was speaking with Shion when they walked into the tea room earlier, accompanied by a young girl and a boy only slightly older.

“Hold on,” Giyu calls when they start to leave.

The children are already running off, but the woman regards him with a gentle smile not unlike her lord’s.

“Yes?”

“...Why do you serve him?”

Her eyes widen a fraction before she laughs, and gives her answer.

“Why?” she echoes, head tilted and eyes heavy-lidded as she turns her gaze to the floor, a small smile on her lips that is now more of fondness than courtesy. “Because Lord Shion is a good man. Because he is someone you would want to fight with, not against.”

She looks up then, all the quiet adoration and deep, oceanic love evaporating in an instant to be replaced with bright cheer as she calls, “Goodnight, Pillar-san!” and shuts the door behind her.

Her bare footsteps pound down the hall after the kids until they disappear as well, leaving Giyu and Sabito to themselves.

“A demon who doesn’t eat people,” Giyu muses.

“And the humans who serve him instead,” Sabito finishes with a smile, and shakes his head. “What have we gotten ourselves into this time, Yuu-chan?”

Chapter Text

Two years have passed, but the water pillars’ encounter with Lord Shion has not faded from their minds. Giyu and Sabito now rarely complete missions together. The Demon Slayers’ forces are spread thin, with Muzan seeming to create more and more. However, the encounters with non-eating demons have become known as well, and a rumor begins to spread. There is a doctor who treats humans and non-eating demons alike, who is working on a cure to turn demons back. Tamayo, they call her, but to find her requires the aid of a human who must enter the white castle and beg for aid.

There is a war among the demons. Muzan’s number one has betrayed him and is building an army of demons who refuse human flesh, demons who remember their lives as humans and protect them as their family.

Which is why, when he senses the bloodlust of a violent demon in a small village to the northeast, he does not immediately kill the boy’s sister.

Muzan has slaughtered their family. The boy tried to save his sister, not having realized what she became or not knowing what it meant. She was starving, she wanted to kill him, to eat. Instead, she chose to protect, and the boy used the only weapon he had in an ingenious way.

It takes skill to throw an axe like that. It takes more than that for a pillar not to notice such a threat until the last minute.

He was distracted.

The boy’s hair reminded him of someone. Someone tall and dangerous, with the ability to rip them to shreds if he so desired and instead offered them tea and a comfortable place to stay. A man who asked for their help, and offered the support of a powerful demon and his army in return.

A man who likely sent the summons that led Giyu to this remote village.

Giyu looks at the children, one unconscious on the ground and the other writhing in his grasp, and frowns.

Just maybe… these two are different.

He lets Nezuko live, and gives Tanjiro a hint.

Perhaps it is time he paid Shion a visit.

When he arrives, the palace is surrounded with wisteria in full bloom. The gardens are bursting with it, purple and beautiful. Dried sprigs line every entryway and are woven along the top of the walls. The sun is setting, and they glow in the pale light.

Clearly, Shion has decided to use flowers as his first line of defense.

Giyu walks through the gates and gardens with no trouble. There is not a single human or guard in sight, which would be concerning if not for the fact that Shion has likely asked them to remain inside for their protection.

“I have been waiting for you.”

Giyu turns to find Shion standing by a graveyard, staring out at the stone monuments which date back centuries. Giyu joins him quietly and follows his grave to a name toward the back, etched in ancient stone with moss. It’s barely legible anymore, but the title reads, “Mikogami Tenzen.”

Giyu waits for Shion to speak. When he does, Shion turns toward him and bows his head. He still wears the veil.

“I thank you for saving the Kamado siblings,” Shion says gently, voice barely above a murmur. “They will be vital to the coming war.”

Giyu watches him. The question rests on the tip of his tongue, awkward and tense. He does not know how to ask.

“I told you once the story of when I began to serve that man,” Shion begins, raising his head.

Giyu nods once.

“Well,” Shion continues, “I did not share the story of how I became a demon.”

He turns, casting Giyuu in a calm gaze through the veil.

“Come with me.”

He begins to walk toward his palace, leaving Giyu to follow.

~+~+~+~

At the end of the story, Giyu sits quietly. The cup of tea in his hands has long since gone cold, but he pays it little mind.

“We failed before,” Giyu murmurs. “What makes you think we can win this time?”

Shion—no, Tanjiro smiles.

“Because we did not have me.”

Giyu raises his eyebrows slightly, surprised.

Shion’s smile widens. He sets his cup down and slowly lifts his hands to his veil. He undoes the golden clasp to remove it, and lays it on the table.

His face is more mature, but a black, fiery scar stretches across his forehead like a demon crest. His features have matured, sharpened with time and age, but he is still recognizable.

Then he opens his eyes, and Giyu’s breath catches in his throat.

His eyes are a beautiful, rich burgundy. His sclera have turned black. Inscribed in both his irises with gold lettering are kanji reading, “Zero.”

“The rumors are true,” Shion, Upper Moon Zero, Tanjiro says. “I have betrayed Muzan. I am the Demon Pillar, the thirteenth demon moon, the bridge between worlds. I will end this bloody, ancient war if it costs me my life, but I will not lose my loved ones again. I will not let you die.”

Again.

“And Sabito…?”

Shion smiles, his eyes softening in a way Giyu thought demons incapable of.

“I met him once, before it all. He helped trained me.”

Giyu’s eyes widen.

Shion bows his head and continues, “I defeated that monster during my final selection, but… Sabito-kun did not become a pillar.”

He died.

“Tanjiro-kun will be brought before the pillars in time,” Shion states calmly. “I will introduce myself to the others then.”

“They will kill you,” Sabito swears, shooting him a look of alarm. “You must know that.”

“Oh, Giyu,” Shion returns, smiling. “Not if I have you. Sabito and Lord Kaguya will be there too. Tanjiro will recognize my scent, but I will not reveal myself to be a demon until after I have Sanemi test Nezuko’s resistance to blood. By then, I will have resisted as well.”

“Still,” Giyu begins, but he is silenced by a raised, clawed hand.

“The Ubuyashiki clan has records on me dating back centuries. I am a pillar. They will listen, and if not… My ranks are not merely for show.”

Suddenly, his power grows, overwhelming, choking. Furious, ready to kill. It burns, but Giyu is frozen to the spot. He’s sure Shion could kill him, but just like the last time, his anger is not directed at him. This is reserved for the man who tore everything from him, for Muzan.

Shion looks up at the moon and grins, a wicked, sharp-toothed smile.

“I have waited four hundred years,” Shion swears, full of patient, destructive rage. “Four hundred years, I held my tongue. I learned to be quiet, to keep my mind blank. I learned not to cry. I’ve barely felt anything but fury and the ache of grief in four hundred years, and that ends soon. Even if I die, I’m taking him to Hell with me.”

Giyu finally understands what the woman meant.

He’s never been more glad to have someone on his side, rather than his enemies’.

Shion’s wrath evaporates as quickly as it had appeared, and he turns back to Giyu with a smile.

“Well, I can’t make my move for a few more years, anyway,” he says softly. “Lady Tamayo is a dear friend of mine. I’m sure you’ve heard of her. We’re working on a cure, but it’s difficult since my blood tends to overpower Muzan’s. If you could try to gather the blood of highly-ranked demons, Giyu-san, it would be a huge help,” Shion says gently, pressing a wooden box into his hands with a well-practiced smile. “Please.”

Giyu startles. He glances down at the box for just a moment, but when he looks up with a response ready on his lips, Shion is nowhere in sight.

In fact, Giyu is now standing knee-deep in a rice paddy, clutching the hilt of his sword in one hand and a small wooden box in the other.

How on earth did that demon manage something like this? Surely, he could not have moved Giyu outside of the castle himself, given the layers of wisteria barricading it. Did he move the castle?

That’s impossible.

Isn’t it?

Giyu marches out onto dry land and decides to open the box. Inside, two small knives with thin glass tubes running down the center rest on red silken padding.

Great. How the hell is he supposed to explain something like this? He has a hard enough time communicating with the other pillars anyway. Sabito is usually there to translate when they misinterpret, but will it be enough? Facing an upper moon who claims to be a pillar, will anything either of them has to say for Shion be enough?

~+~+~+~

When Shion returns to the upper floors of his castle after moving the grounds, he finds Tamayo bent over her work with Yushiro nodding off at her side. He looks up as Shion enters, but his expression quickly shifts from alarm to relief.

"How long do we have?" Tamayo inquires.

Shion's smile fades into a thoughtful frown.

"Approximately three years," he admits.

“And how did the water pillar take it?” she asks, dipping her brush in the inkpot beside her.

“I believe he will lend his aid,” Shion admits as he looks down at her work.

She is doing the math for a new configuration of the chemicals involved, and it all looks far too complex for him.

“Yushiro, you will need to infiltrate the Demon Corps during the final battle,” Shion states calmly. “Your duty will be to save Zenitsu Agatsuma after that child defeats Upper Moon Six. Other than that, your roles are largely supportive."

“No,” Tamayo argues firmly, drawing their gazes to her as she keeps her head bowed. “I will deliver the serum to Muzan’s bloodstream and attempt to keep him immobilized during the final battle.”

Yushio opens his mouth to object, but she continues.

“I cannot allow the task to fall upon someone else. I will not stand back while others risk their lives.”

“Shion could deliver the serum!” Yushiro argues, gesturing to the man.

“There is too much at risk to lose Shion so early in the battle. I am prepared to lay down my life if it means defeating Muzan.”

Shion nods his thanks, but Yushiro grits his teeth.

“Now is not the time for this conversation,” Shion says gently. “How are the patients?”

“Most of them are resting right now,” Tamayo replies as she sets her brush down. “Muzan’s attacks have been brutal, but thanks to your blood, they will survive.”

“That’s good to hear,” Shion sighs, turning away. “I will prepare a safehouse for you two in Tokyo. You should be able to stay there for some time.”

“Shion,” Tamayo begins to argue.

He shakes his head and says, “It’s safer for you both there. I can escape if my castle falls, but I can’t save everyone in it. Once the patients are safe, you need to hide somewhere else.”

She stands up and sighs, “Understood.”

She walks around the table to him and pauses beside him, casting him a small smile. Shion returns her gaze calmly. She leans in to whisper in his ear, and he bows his head to hear it.

“If we leave so soon, will you spend tonight with me?”

Shion smiles back and turns toward her just enough to say, “Of course.”

Yushiro rolls his eyes and mutters something about tending to the patients before he walks away, leaving them alone.

Shion turns fully to take her hand in his own and brushes her hair behind her ear. She leans into his touch with a gentle smile and holds his hand against her cheek. She is so beautiful it makes his heart ache.

Shion has existed for centuries, yet he still remembers the day he met her. Not only as Tanjiro, but as himself, as Upper Moon Zero and Lord of Himeji Castle.

He had slipped through Yushiro’s defenses like a ghost and alighted on their windowsill. Tamayo assumed he had been sent to kill them, as was reasonable. He just managed to convince them not to attack him just yet by showing them enough of his presence to know they couldn’t win, and asked for their help much the same way he did the water pillars.

Tamayo took it much better than Yushiro. Especially after she heard his story.

"Let me make sure I'm understanding this correctly," Tamayo had said, quiet. "You were a demon slayer, who fought Muzan. He tried to kill you by flooding your system with his blood, but your body adapted and you activated a blood technique that allows you to manipulate the fabric of time and space itself."

Shion smiled like it was all perfectly reasonable.

"You overused your ability because you didn't know how to control it yet, and got thrown four hundred years in the past,” Tamayo continued. “Your body adapted to allow you not to eat human flesh and you conquered the sun, which is why Muzan has let you live so long. You've been living in Himeji Castle and steadily gaining power for over two hundred years?"

"Yes," Shion replied with an easy smile.

"And you've been working behind his back this whole time?" Tamayo had realized, her voice barely above a whisper. She stared at him in awe and asked, "What is your name?"

Shion grinned then, and told her.

As he left, he handed her a vial of his blood and said, “I have waited two hundred years for someone willing to turn against him, my Lady. It would be a shame not to have you beside me."

They’ve been close friends ever since. At some point over the past hundred and fifty-odd years, they became something more than that. They haven’t spent every moment together, but the few stolen visits have been cherished by both.

It is easy to slip into an intimacy such as they have with the histories they do.

Chapter Text

Be careful.

Those were Tamayo’s parting words, delivered with a kiss. Shion nodded gravely and shut his eyes, tapping into the reservoir of his power to transport them safely.

They land in an empty alleyway in the streets of Tokyo.

Then he departed for the semi-annual Pillar Summit.

Shion arrives before daybreak. Lord Kaguya invites him in for breakfast and takes great pleasure in getting to know the demon known as the leader of a revolution. Shion enjoys meeting the latest Ubuyashiki family head, so mature for a child. Kaguya seems to recognize that despite Shion’s status as a pillar, he is no more one of Kaguya’s children than a lion can be a mouse’s prey.

Shion is having tea with Lord Kaguya when the demon slayers arrive. Two children are forced into submission on the ground before them by a kakushi, one human and the other, a demon. The pillars begin to argue, and Shion smiles. Clearly, the changes he’s made haven’t altered their personalities. The only difference is that it’s Sabito who speaks up in Tanjiro’s defense instead of Shinobu.

“It seems our guests have arrived, Lord Kaguya,” Shion comments with amusement.

“Indeed,” the man responds with a smile, and bows his head.

They rise from their seats slowly, their robes settling around them as they do. Neither wears a blade, but their power is undeniable nonetheless. They are both the leaders of armies for a reason.

Kaguya’s children guide him to the front room, where the arguing is loudest through the rice paper doors. It sounds like Sanemi has made his move against Nezuko.

“Stop!” Giyu’s voice shouts over Tanjiro’s scream. “The Master will be arriving soon.”

From the ensuing thud of Tanjiro’s skull, followed by two more thuds and the clatter of a sword, it doesn’t sound like his plea is successful.

Sanemi groans.

“If you can’t tell the difference between good demons and bad,” Tanjiro Kamado begins softly, anger laced through his tone like tempered steel, “you should quit being a pillar!”

“Bastard,” Sanemi growls, picking up his sword again. “I’ll crush you!”

Then the sisters open the doors and announce their arrival.

Lord Kaguya steps forward first and greets them warmly as though they are his children visiting for the holidays and not men and women in the midst of war. Shion is amazed by how quickly the pillars pull themselves together and kneel before their master. The sight even makes him smile.

He catches Tanjiro staring, and gives him the slightest of nods before Sanemi forces Tanjiro’s face into the gravel.

Ouch, he remembers how much that hurt.

Shion returns his gaze to the other pillars behind his veil. He had forgotten some of their faces. To see them all here, alive, is… almost too much to bear.

He must stay strong. This is his moment to prove himself. He didn’t go through all the trouble of asking Yushiro to conceal his horns to lose composure over something like this.

Alive. Shinobu, Tokito, Sabito, Rengoku. Alive, breathing, not covered in blood or dying before his eyes.

Kaguya’s daughters guide him forward, and Shion follows him into the sunlight. He loves the warmth of it on his skin and so rarely gets to make use of it, since so much of his business must be conducted in the depths of night. He missed this, this ability to bask in the light.

“Good morning, everyone.” Kaguya smiles, turning his head up toward the sunlight for a moment to muse, “The weather is beautiful today. I wonder if the sky is blue…”

Then he looks down to continue and his tone takes on a more serious note.

“It pleases me to see we’ve made it to our semiannual pillar meeting with no personnel changes.”

Where Sanemi’s tone was violent and aggressive before, now he speaks with humility and grace, “I am pleased to see you in good health as well, Master. I fervently pray for your continued good fortune.”

“Thank you, Sanemi,” Kaguyra returns kindly.

“Before we begin the meeting,” Sanemi continues, raising his head to reveal wide, furious eyes, “would you mind enlightening us about this swordsman, Tanjiro Kamado, accompanied by a demon?”

“Right,” Kaguya replies, soft. “I apologize for startling you all. About Tanjiro and Nezuko… I’ve sanctioned their situation. Nezuko is not the first demon to be accepted by the Demon Slayer Corps, nor is she the first demon to refuse human flesh.”

The pillars each look up, concealing their surprise in every way but their eyes.

“Do you mean the rumors about non-eating demons, Master?” Shinobu asks softly.

“They are not mere rumors,” Kaguya states firmly, still wearing a smile on his face. “Please, allow me to introduce to you the tenth pillar among the demon slayers: Shion, Lord of Himeji Castle.”

He gestures toward his guest, who steps forward with a smile and bows his head to his fellow pillars.

“It is a pleasure to meet you all,” he says gently. “I’m afraid I cannot reveal my face to you, but I have asked Lord Kaguya to sanction the Kamado siblings’ situation. I also interfered in Final Selection a few years ago,” Shion admits with a nod toward Sabito and Giyu. “If I may, Tanjiro, will you bring your sister into the shadows here for me, please?”

Sanemi, startled by the news and Shion’s request, lets Tanjiro stand up and shuffle forward with the box which holds his little sister. Shion bows his head in thanks and calls Sanemi forward next.

“Sanemi,” Shion calls gently, “my blood is insufficient, so would you please?”

Sanemi blinks in surprise. He nods stiffly and comes forward, rolling up his sleeve as he steps up into the shade. Tanjiro steps aside as Sanemi draws his blade across the back of his forearm. His blood begins to spill upon the tatami floor, rich and scarlet. Shion covers his nose, and ignores the way Tanjiro is staring at him.

He’s getting dizzy. He has resisted temptation for four hundred years, satiating himself with sex and alcohol instead. But at the scent of this, his head starts to spin.

Oh, what would just a taste be like?

Shion bites his tongue for the first time in two centuries to hold himself back. He knew this part would be difficult.

The pillars watch as the box shakes and a young girl crawls out, her eyes a light pink with slit pupils. She growls around the bamboo gag in her mouth, glaring at the blood dripping from Sanemi’s arm.

Nezuko hesitates, and turns her nose up in disgust.

Her action allows Shion to remember where he is and why he came here, and he exhales. He feels shaky and out of breath, but who can blame him? It’s rare even for marechi.

“There you have it,” he says, a little more breathless than he would like. “Nezuko Kamado refuses even marechi blood of one who has antagonized her. She will not eat humans, and if she does, both current water pillars, Sakonji Urokodaki, and Tanjiro Kamado will atone by committing seppuku.”

Shion bows his head and turns away, moving to clasp his hands in front of him between this sleeves.

Sanemi turns, reeking of shock and confusion.

“What the hell?” he asks, staring at Shion. “Why do you look drunk?”

Shion looks back, and grins. Sanemi’s eyes widen, Kanroji gasps, Rengoku, Iguro, and Shinobu reach for their swords. Giyu and Sabito step forward, and Lord Kaguyra raises his hand to still them all.

“You have all heard rumors of a demon working against that man,” Shion explains, turning toward the other slayers. “An upper moon, no less. Do you wonder why I have never been mentioned in the meetings, despite my absence?”

Their silence rings, and his grin widens. He allows Yushiro’s wards to fall and feels his presence grow with his height and his horns, allowing his nails to blacken and elongate. The pillars shift on their feet, uneasy, but their master’s firm glare keeps them still.

“I am the Demon Pillar, Upper Moon Zero,” Shion growls, watching each of their swords. “I am both demon slayer and demon, pillar and upper moon. I have waited four hundred years to kill the man who turned me into this, and served him all this time. We finally have a chance to defeat him now, and I will not let it go to waste.”

“I am intrigued by this turn of events!” Rengoku exclaims, “But how can you prove you’re not working against us?”

Shion’s smile widens further.

He tilts his head as he admits, “I can’t. All I ask is to help you defeat Muzan for all he has done. Giyu-san and Sabito-san are more aware of the circumstances, having met me once before.”

“Your hand,” Kanroji breathes, staring at him. “The sun didn’t burn you.”

“No,” Shion replies. His smile softens and he tells them, “I am the first demon in history to overcome the sun, but not the first I’ve known.”

“So you’re asking us to help you defeat Muzan,” Tanjiro Kamado affirms with a furrowed brow. “And you want to protect my sister.”

Shion smiles and inclines his head slightly to say, “Put simply, yes.”

“Why?” Tanjiro asks, frowning in confusion.

Shion looks at him calmly. His smile falls, replaced with a carefully neutral expression. Four hundred years ago, he looked like this. How much has changed since then? Would they even recognize the difference?

Shion takes a deep breath and lets it out slow.

“Nezuko Kamado refuses blood that makes even me tremble. I believe she may be even stronger than I am, and more capable by far.”

He bows his head to remove his veil and opens his eyes to the true sun for the first time in years. The demon slayers’ eyes widen, some with more shock than others’.

That man has killed hundreds of people trying to replicate my abilities in demons who have already lost their humanity,” Shion continues gravely. “I have found a way to help demons who have not yet consumed human flesh regain their humanity, but it is an arduous process and rarely results in the manifestation of this strength. Nezuko-chan may be able to overcome the sun, which is why it is vital that she be protected by the Demon Slayer Corps and kept out of his reach. It’s dangerous enough for him to have had me all this time.”

None but Giyuu and Kaguya seem to recognize him. Good. He’s sure the scar-turned-mark helps. His face has matured, his cheekbones sharpened in a nearly inhuman way, and his hair is much longer. At best, he looks like an ancient relative.

In a sense, he supposes he is.

“What was your identity as a human?” Iguro questions, eyes narrowed.

Shion keeps his face carefully neutral. Even after all this time, lying is still incredibly painful. He cannot do so without screwing up his face, but a half-truth may suffice.

“I am a descendant of the Breath of the Sun user.”

Those who know what that means, startle.

“I have valuable information on the twelve demon moons,” Shion continues, trying to draw the conversation away from his identity. “I know that man’s only weaknesses are the sun and wisteria, which is why my palace is surrounded by both.”

“You really intend to fight him,” Kanroji breathes, wide-eyed. “You, an upper moon.”

Shion fixes her in his stare and watches her jump. He knows she cannot move. He knows his very presence is overpowering, overwhelming. He has perfected it to be so.

“I would not come here, to the heart of the Demon Slayer Corps among the strongest humanity has to offer, if I did not.”

He has made his introduction. He has shown himself to them, and they will know he is on their side when they meet again. It is time for him to leave.

“Wait,” Tanjiro calls, because he was never able to keep his nose out of trouble.

Shion would admire that about his human self, if it weren’t what got so many of his friends killed.

“What made you want to protect humans?” he asks with such an earnest frown.

Well. Shion owes him that much, at least.

He crosses to kneel before the boy, expression calm and serious. Giyu is watching him with sharp eyes, and the rest of the pillars are smart enough to keep their distance.

“You will understand in time,” Shion tells him gently, resting his hand atop Tanjiro’s head to ruffle his hair like he used to his younger siblings’. “Whether we win or fail, you will understand.”

Shion straightens up, takes one more look at the demon slayers, at their living faces, and smiles.

Time freezes around him. He crosses the courtyard to leave messages for each of them in their pockets, small scrolls written carefully.

Sanemi’s reads, “Forgive your brother. He doesn’t hate you.”

Shinobu’s, “Your sacrifice will be worth it.”

Giyu, “Don’t let the sacrifices of those who have died go to waste.”

Each of them vital, each of them powerful.

Afterward, he casts them one more sad smile before he turns his back and walks away. After all, he has an army to gather.

~+~+~+~

Shion debates lending his aid to Rengoku on the train for days. In the end, he gives in.

The kids cannot be allowed to see Shion again, but they cannot watch Rengoku die, either.

Shion watches from afar under a heavy disguise when Enmu’s pawns put them to sleep, and the Kamados help them all awaken. Tanjiro and Inosuke destroy Enmu, and all seems well.

Until Akaza’s presence appears.

Shion decided to deal with this as quickly and quietly as possible. If he can prevent Akaza from reaching the train, then all will not be lost.

Of course, nothing ever goes according to plan.

The train is stalled and derailed after Enmu’s death. Rengoku and the demon slayer kids help evacuate the civilians. Shion intercepts Akaza in the shadows of the forest, but a battle between demons will always be pointlessly gruesome.

Unless one holds a demon slayer’s sword.

Akaza’s eyes widen in fear when Shion draws his blade. He begins to stammer, but Shion only has so much time to cut his head off before Muzan will use his link to check Akaza’s thoughts. And so, he lunges forward.

Akaza’s head falls with a dull thud, and Shion kneels before him to pray.

“You! Traitor! How dare you?!” Akaza screams.

Shion ignores him, standing once he finishes the prayer. He looks down as the demon crumbles, tears welling up in his eyes as he remembers his wife, his father-in-law, his life. He begins to sob, and Shion can’t help the murmured apology that escapes his lips.

Just as he prepares to leave, a usually booming voice calls his name calmly.

“Shion.”

He turns, raising an eyebrow at the pillar who stands before him. Rengoku stands still at the edge of the trees, his sword raised. His expression is firm, but his eyes burn with their usual fire.

“Why would you kill your own kind?”

Shion regards him for a long moment before he deigns to give an answer.

“Because it saved yours.”

Rengoku blinks once, but doesn’t move. His gaze flickers to Shion’s blade, which he quickly covers with his robes.

“You have a demon slayer’s sword,” Rengoku comments.

“I am a pillar, Rengoku-san.”

“And an upper moon.”

Shion smiles.

“Until next time, Rengoku-san.”

With a bow, Shion halts time and disappears before the children come running over.

He doesn’t have time to explain anything more to them right now, and he certainly doesn’t have time to answer young Tanjiro’s many questions.

Nevermind how he might feel at the sight of Inosuke and Zenitsu once again alive and well.

Shion goes home before he allows himself to think about that.

Tamayo is waiting for him.

After the Kamados found her and Yushiro, they returned to the castle. Shion has been glad for it, except when he comes back from doing something reckless she gives him this look.

“It shouldn’t interfere with the plan,” Shion promises her as he crosses the room to hug her.

She allows it, and gives him a kiss before she tells him, “Still, that was too close. What if Muzan found you? Or the demon slayers figure out who you used to be?”

He sighs and holds her close, letting his eyes close as he breathes in her scent, fragrant and sweet.

“I’ll handle it.”

He never did like sharing his burdens.

Chapter Text

Shion knows the moment things are set in motion. Kaguya’s crow comes bearing the message that Muzan would arrive tonight, and Shion departs immediately. Tamayo and Yushiro stay by his sides, calm and solemn. Tonight, they may all be marching to their long-awaited deaths. It is better to do so as a family than all on their own.

Tamayo takes Shion’s hand as they near the estate. He gives her a small smile, and then lets her go.

He and Yushiro stand back as she goes into the estate alone armed with only her syringe and fights tooth and nail to hold Muzan down.

They watch as the pillars and the rest of the demon slayers arrive, Shion’s army standing in the shadows ready to fight. They all seek revenge.

The outcome of this war determines many things, but most of all, it determines who is left.

If all goes according to Shion’s plan, they will lose many fewer lives than they did last time.

For once, thank god, everything goes according to plan until the very end.

Shion feels it the moment his wife has died, absorbed by Muzan. He grits his teeth, and leads his army with a war cry that rattles bones. The demon slayers freeze in panic until they see the demons charge past them and begin working with them, pushing past obstacles and aiding the wounded. Shion follows his nose toward Muzan and sends Yushiro to find Zenitsu before it’s too late.

At the end, they bring Muzan to the surface. Tanjiro apparently arrived with Rengoku, which should hardly be a surprise. The pillars attack Muzan as one, and Shion moves.

“You,” Muzan snarls when Shion pulls his younger self out of harm’s way.

Shion bares his teeth as he pushes Tanjiro behind him, readying his sword.

“No matter,” Muzan sighs, drawing himself up to his full height. “I will destroy you, too, Shion.”

Shion laughs.

He lunges forward faster than the eye can see. Muzan takes a half step back when Shion appears in front of him, snarling like a wild beast. Muzan tries to kill him, but Shion flickers out of the way and reappears behind, beside, in front, all around him, searching for an opening, for the opening thread while keeping the others safe. He takes up all of Muzan’s attention, forcing him to focus only on keeping the pillars at a distance and no more.

He will win. He will not fail again.

Muzan snarls with impatience. He reaches out to grab Shion’s throat and gets his arm cut off for the attempt. When his eyes widen in surprise, Shion grins. His gaze is hard and unforgiving.

“Do not think you have won simply because I do not stand for war,” Shion says softly. “You will die a thousand deaths before you will have paid for the millions you caused. I will burn you from this earth, and you will be greeted by no lost family on the other side. You will die a lonesome death, and that, perhaps, is what you fear worse than no death at all.”

He brings his sword down. Muzan’s eyes widen in surprise, in fear, but the battle isn’t won until the sun shines on them again. Shion has to keep him busy, has to keep the others safe until then. Muzan cannot kill him; he isn’t capable. The only weapon he has is only truly dangerous against the humans, for any more blood Shion absorbs will be overpowered shortly.

Shion takes many hits by the time he can feel daybreak coming. Muzan’s attacks become stronger, more desperate, more erratic. He does not let up. Shion does not falter. He is exhausted, he’s bleeding and the extra force of Muzan’s poisonous blood courses through him, throbbing. His lungs and limbs ache, but he cannot afford to lose. Not now, not after everything.

Tanjiro is safe. Giyu is safe. Sabito, Rengoku, Tokito, Himejima, Kanroji, Iguro are safe.

Hold on until daybreak.

The sun finally reaches over the horizon and sets the sky ablaze. Muzan screams, targeting Shion with everything he has but Shion has been training for this for too long. He has awaited this day for hundreds of years.

He feels no sympathy when the sun burns Muzan to a crisp. He gives him the same amount of mercy Muzan lent every one of his victims and their families: none.

Shion doesn’t even bother to pray.

Muzan was a creature who should have never been allowed to exist. He does not deserve the respect of the dead.

Shion can feel the demon slayers closing in. They watched the battle from afar, kept at bay by Muzan’s poisonous whips, but now they can get close enough to see. Shion left his veil at home. He collapses on the ground as soon as the threat is gone and looks up through blurry eyes as the pillars come into view above.

“Shion,” Giyu greets softly, and pretends not to notice the way the other pillars startle at the sound of his voice.

Shion smiles and allows Giyu to take his hand. He looks over at Tanjiro, unharmed, and shuts his eyes.

“Hey,” Shion greets, breathless and far too tired to move. “How’s Nezuko?”

“Good,” Tanjiro sobs, nodding. “Thanks to you.”

“No,” Shion replies, smiling even as he wipes the boy’s tears from his cheek. “It’s thanks to you.”

He doesn’t need to open his eyes to know Tanjiro is frowning.

“What do you mean?”

Shion would like to say he can feel himself slipping away, but that is not the case. He is simply going to fall asleep and awaken to an empty castle as a demon with no way to return to being human. No way to die.

“I need you to do me a favor, okay?” Shion asks softly, tightening his grip on Giyu’s hand to keep himself awake. “It’s going to be difficult, but I can’t go on like this. My wife, Tamayo… She lost her life for this. My children… The other demons are dead. Let me meet them on the other side.”

“But-!”

“Please,” Shion begs, finally opening his teary eyes to the Water Pillar. “There is already one Tanjiro Kamado in this time. I saved everyone I could. Now let me die like I should have so long ago, when I watched you all die the first time.”

“The first time?” Rengoku echoes, wide-eyed as ever.

“Please,” Shion requests again, softer this time. “There’s no time.”

He can’t stay awake much longer, and it will be difficult to kill him once he falls asleep.

“Alright.”

Sabito steps forward, sword in hand.

“Thank you,” Shion laughs, breathless.

Shion closes his eyes again. Giyu’s hand is cool and comforting. Tanjiro is crying beside him, asking questions Shion doesn’t have time to answer, questions Tanjiro will learn the answers to in time. Finally, finally everyone is safe.

Finally, they’ve won.

The blade comes down quietly. He hardly feels a thing.

“Shion?”

He opens his eyes. He’s standing on his feet in a black abyss. Tamayo stands before him, her beautiful features set in a frown.

He pulls her toward him and smooths them with a kiss.

“We won,” he tells her, breathless. “He’s dead. They’re alive.”

She smiles, and takes his hands in her own. He opens his eyes to meet her beautiful gaze, and smiles a genuine smile. He starts to get choked up, and lets out a laugh that sounds a little too close to a sob.

Were his emotions always this strong?

“Let’s go home, dear.”

He has waited four hundred long years for this. He has waited four hundred years to finally be at peace once more.