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Osmotic Assimilation

Chapter Text

A ground-shaking rumble filled the concrete halls of the bunker Hisashi Midoriya called his primary base of operations. At 6 foot 2,even with a more lean body type, he cut an impressive figure; with a well tailored suit being his preferred outfit, his presence alone demanded respect.

However, with his gray hair looking like he’d just crawled out of bed, tie horribly tied (it always took him at least 3 tries), shirt untucked, and sporting a mild 5 o’clock, it was jarring to those that knew him to see him so unkempt. The international crime lord known as All-for-One’s careful facade was fractured, and Kurogiri knew it.

“That no good muscle-brained idiot! How the hell did he even find this base?! My information said I had at least 3 years before he found me! Four, if I played my cards right! Kurogiri, how’s young Tomura doing?”

“I’ve gathered all of his things and he’s just in the other room. Do you want me to warp Gigantomachia here? I have his coordinates and am waiting for your order.”

Hisashi finished packing the last of his personal belongings and threw the suitcase at Kurogiri. Thinking for a moment, he shook his head.

“No, actually, I’ve got a more important job for you. If this goes the way I think it will… Machia’s going to be needed elsewhere. Remember these numbers, Kurogiri: 35 degrees, 39 minutes, 13 seconds north. 137 degrees, 25 minutes, 49.1 seconds east. Do you have those numbers memorized?”

Kurogiri gave a short bow. “Yes sir, and what do you want me to do with those?”

Sighing, Hisashi started straightening his appearance.

“You, Shigaraki, and Gigantomachia are to convince the people at that location of their own free will, to get far, far away from Japan. If I’d had the expected three years, I could have ensured their safety by… silencing those who’d seek to harm them in my absence, but it’s too late for that now. The briefcase has a letter that should help.”

The narrowing of the yellow lights of his eyes was the only indication of Kurogiri’s distaste for the wretches his master has had to keep in line. 

“Very well, by your leave I shall get the young master out of here.”

Finally getting his tie properly done and straight, Hisashi pulled a photo out of his pocket:one of him with a young woman with dark green hair, and a toddler with his messy curls and the woman’s hair color.

“You’re free to go Kurogiri, live long, and prosper.”

“Sir, is this really the time for jokes?”

Chuckling, Hisashi let the embers build in the back of his throat.

“I always was partial to gallows humor, old friend.”

Breathing flames onto the photo, he watched as the last of it disappeared into ashes.

If someone were familiar enough with Kurogiri’s unique biology, the droplets of light that disappeared into the air might have been considered tears as he closed the door behind him.

“So, you’re saying he has a hidden quirk?”

Midoriya Inko let out an internal sigh of relief. Though her husband had his secrets, he had let it slip that any of their kids had a high chance of being quirkless. Though hidden quirks weren’t uncommon, there were usually small signs that they existed.

“Yes ma’am. We aren’t quite sure what it is exactly however. The best we can compare it to is an adaptation quirk. His cells are very adaptable, and seem to react to stimulus such as other organic material. We do know however that it is a mutation quirk, not an emitter.”

Petting her sons hair, (so much like his father’s), she couldn’t help the worried thoughts trailing in the back of her mind. She couldn’t be more thankful he’d worn himself out the night before watching the hero news and had fallen asleep while waiting on the results.

“Anything else I need to know doctor? My son wore himself out the night before and my husband was wanting to hear the final verdict as soon as he could. He even told me he’d stay up all night in America if he had to.”

She gave  a soft chuckle thinking of Hisashi pacing back in forth in an american hotel waiting on her call, even if he had important meetings early in the morning.

“No ma’am, that’s all we can say for sure right now. I’d suggest  bringing him in again next year if nothing obvious shows up, or visit a specialized lab if you want to know more. Quirks like this tend to be very slow acting in their infancy, so we might not see anything for a long while and without more extensive testing.”

Bowing to the doctor slightly, she picked up Izuku, careful not to wake him up, 

“In that case, thank you for putting our worries to rest, and have a good day.”

As she got started towards the train station, she managed to fish her cell phone out and dial up Hisashi’s number. Normally he picked up the phone before the third ring, but as it hit voicemail she couldn’t help the spike of worry that pierced her heart.

It wasn’t until they got home that her worries really made themselves known.

Though the purple smokey figure might have been eye catching for a second  to most, the suit he was wearing really held her focus. Her husband only wore the highest quality clothing he could find, and the suit this figure was wearing was the same make. The fact that he stood up from the bench he was sitting on the second he saw her didn’t help, either.

“Mrs. Midoriya I assume?”

The voice was deep, and had an echoy quality to it, even with how quiet he spoke to not wake her son.

“Yes, I am. Why are you asking? And who are you?”

She had managed to fish her keys out and was just about to unlock the door when she heard the words she hadn’t  wanted to hear for another 40 years, and even then they would have been too soon.

“It’s about your husband, ma’am...”

Having carefully set Izuku into bed, Inko headed back to the dining room where she had quietly  asked the man to take a seat. Grabbing the tissues she knew she would be needing shortly, she took a seat across the table from him.

“Y-You’re saying something happened to my husband?”

Kurogiri did his best nod, standard to those who didn’t know him.

“I’m… unsure at the moment, truthfully. How much do you know about your husbands work?”

Dabbing at tears, Inko did her best to recall what all her husband had let slip in their years together.

“I knew h-he was very secretive about it. I knew h-he h-had a lot of meetings, and that some people didn’t like what h-he did.”

Kurogiri let out a sigh at that. He couldn’t blame his boss for not telling his wife, but this would complicate things… quite a bit.

“Midoriya-san. There’s no easy way to say this, but your husband was the king of Japan’s criminal underworld.”

If she were holding something, she’d surely have dropped it in disbelief.

“My h-husband was a WHAT?!”

Covering her mouth, she looked at the door to Izuku’s room to listen for any noises, and relaxed when there weren’t any. Turning back she glared at Kurogiri with teary eyes.

“Now Kurogiri-san, I may be a housewife, but I don’t appreciate some stranger coming in and badmouthing my husband and insinuating that he’s some sort of criminal psychopath!”

Kurogiri was worried this would happen, and carefully,  moving slowly to not scare the poor woman, he dropped a briefcase onto the table, warping it in from where he had left it at their nearby hideaway.

“Hisashi was a good man, that I don’t dispute you on, but I’ve known him for over 30 years, and I can guarantee you, he had his hands in many cookie jars. He wanted me to give this to you.”

Opening the case, Inko saw several of Hisashi’s personal travel items, but on top was an envelope that simply read “I.M”. Pulling it out, she broke the seal to withdraw a letter.


To my angel,

If you are reading this, then I fear something has caused a worst case scenario for me to not be telling you this myself. Chances are, I gave this note to a long-time friend of mine named Kurogiri. He might have a young charge with him named Tomura Shigaraki, depending how much of a hurry he, and by proxy, you must now be in.

I’d hoped this wouldn’t happen for many, many years, but I wrote this as a sort of just in case. The man you knew was not fake in the slightest, but many details of my centuries long life have been kept from you, and not without good reason. I had hoped to keep work and home separate as much as I could.

I didn’t mean to become the crime lord I am, but as the years wore on, I discovered the best way to control crime was to be in charge of it. I do not expect you to approve of my methods, but you can’t deny some of the results. Human trafficking is basically non-existent now, but I have… ‘associates’ who have repeatedly wished to change that, along with several of the other policies I enforced with an iron fist.

If something happens to me, they will come for you, even if they don’t know for sure that you exist,  and I simply can’t take the risk. Get far, far away from our home, I have another that I purchased with enough proxies and relays that no one should be able to find it. I’m so, so sorry you had to find out like this, my love, but I was doing what I thought was best, and even now am  doing what I hope is best for you, and for our son.

With love, H.M/All For One.

By the time she finished reading the letter, her tears were running freely and smearing the once-dried ink.

Kurogiri’s smoky appearance didn’t change as the woman broke down in front of him. But he did push the box of tissues closer within her reach.

Inko slowly managed to get her breathing under control, wiping the streaks from her cheeks.

“Is th-that why you’re here? The sa-safe house he mentioned?”

“Yes, your husband had a bodyguard that he wanted me to have you and your son meet with. However, with the way things unfolded, he also wished for me and my charge to accompany you as well.”

Wiping the tears from her face, Inko felt like the entire world was weighing on her shoulders.

“How quickly do we need to leave?”

“It would be wisest for us to leave within the day; my quirk would let use leave this very moment if it was required.”

Standing up, Inko put the letter back in the case before closing it back closed.

“Give me a few hours to grab everything and get Izuku ready. Don’t mention any of this to him please, I’d rather know for sure before we tell him.”

Standing himself, Kurogiri used his quirk to open a portal against one wall.

“Very well, I’ll be back in 2 hours, as I imagine young Shigaraki is getting hungry. I shall see you then.” And without another word, he was gone.

As the wisps of smoke faded away, Inko began the daunting task of packing the essentials and gathering the resolve to wake up Izuku.

Chapter Text

It was taking all of All for One’s focus to keep the meat-head known as All Might that was after his blood out of reach. Although  he was missing several of the quirks that would have helped him keep up. His air resistance quirk was ensuring that All Might had to actually land a blow in order to send him flying instead of just punching the air.


As they broke apart from another flurry of blows that they both narrowly dodged, Hisashi could really feel the toll the fight was taking on him. With his base in shambles around him, he couldn’t help but be glad he’d sent the others away. He had so many quirks that he’d been planning to get for this inevitable clash: danger sense, improved reaction, and impact recoil would have all been handy.


All Might wasn’t unscathed himself, but neither of them were seriously harmed yet, and with both of them short of breath, he unleashed his secret weapon. Taking a deep breath, deeper than most lungs could physically hold, he unleashed a wall of fire, so bright in its intensity that anyone looking at it was bound to be seeing spots, even if for only moments.


Moments were all Hisashi needed, using Spring Leg, Air Push, and Drill Arm, he launched himself through the wall that he had intentionally stopped short of making All Might dodge, finally landing a  hit on All Might. He enjoyed the widening of his opponents eyes as his arm bore itself into his side, the edges of the drill hooking and pulling it in that much deeper, until the drill tore itself out of his side in a spray of blood.


Letting his arm revert to normal, he watched as All Might, the symbol of peace, the world’s number one hero, collapsed to his knees, a gaping hole in the left side of his torso. A little lower than he would have liked, but certainly a wound that would be fatal before long.


Hisashi stayed on guard as he watched All Might attempt to stand, releasing bloody coughs as he almost got to his feet before collapsing into the slowly forming puddle beneath him, blood gushing from his mouth as well as his side. As much as he’d like to sit and watch the hero bleed out into the dirt, it was only a matter of time before helicopters showed up and his face would be on national TV.


“Just like your late master All Might. All talk and with a relentless drive to pursue me, but yet again it is the hero’s blood on the ground while I stand all but untouched. Now if you excuse me, I have somewhere to be.”


As he walked away from the soon-to-be-corpse, he reached for his phone to dial Kurogiri. In another world, a world where he had the four years he’d expected, with enhanced speed and danger sense, he would turn in time to see All Might charging him, organs trailing behind him in the wind. With his enhanced speed, he would manage to duck ever so slightly, losing his sight but keeping his life…


Here, and now however. All for One only managed to turn slightly, only caught a glimpse of the fist headed towards his face before he knew no more.


As All Might stood there, hole in his chest, he felt the urge to vomit even though he wasn’t sure he was still able to.. He’d avenged his master, yes, but he felt no satisfaction from doing so. All he felt now was hollowness that he hoped was only coming from the giant hole in his side.


But, as he stared down at the cooling corpse with a blood splatter for a head, he knew the gruesome sight wouldn’t be as pleasant to see in his dreams as he had once hoped.


“Izuku, honey, it's time to wake up.”


Gently shaking her son’s shoulders, Inko hoped she was making the right choice. But as she heard the news reporters mention a “Freak gas plant explosion,” she couldn’t help the feeling of dread that had settled like a rock in her stomach.


“Mmmr, yeah mom?”


As her four-year-old son opened his eyes and let out a yawn that made her want to just wrap him in a blanket until this all blew over, she took in a deep breath to collect her thoughts  and tried to figure out a way to shatter her son’s entire world.


“Your father… he had an accident at work, sweetie. We’re going to be staying with some friends of his for a little while.”


Izuku’s eyes widened a bit, before furrowing into what she called his “Hisashi face” as his brain started processing what she had said.


“Is… is Dad ok?”


Oh, her precious baby… no cheers about getting out of school, no worries about seeing Katsuki and their play date tomorrow. His first thought was to see if his dad was ok. He truly had the heart of a hero… 


She wrapped her son in a gentle hug.


“I don’t know Izuku, we should find out soon though. Is there anything you want to take with us? I’m not sure when we’ll be back.”


Izuku took a moment to think. “My drawing notebook and my All Might figure and uh… my pajamas?”


Inko couldn’t help but let out a snort despite the situation.


“Sure sweetie. I was planning to take your pajamas already, but we can take your notebook too. Do you want to help me fold the clothes while we pack?”


He smiled, perking up instantly at the idea of helping his mom. 


“Never fear! For I am here! To help fold clothes!”


When Izuku slung on his backpack, he expected his mom to lead them out the door and to the car, but instead she asked him to sit on the couch while she glanced at the clock every few minutes. Quickly getting tired of waiting, he decided to amuse himself by kicking his feet into the couch as he rocked back and forth.


However, when  purple smoke started pouring out of a rift in open space, he lost his balance in his surprise and tumbled over with a shout.


A smokey figure in a suit stepped out of the rift, and Izuku  couldn’t help but stare in wonder. He’d never seen a quirk quite like it before.


Kurogiri looked down at the source of the shout, narrowing his ‘eyes’ as they fell upon the All Might onesie Izuku was wearing before looking back over at Inko.


“Are you ready, Mrs. Midoriya?”


His voice had its usual haunting echo to it, upon hearing it most children backed away in fear. However, his new young charge unlike  most children. 


“Woah…. So cool!”


As Inko grabbed their bags, Izuku walked up to Kurogiri with his backpack on his back, bouncing from one foot to the other in excitement. Kneeling down, Kurogiri looked him in the eye.


“So, you’re young Izuku I presume?”


Nodding so fast Kurogiri was worried he’d hurt something, Izuku finally let loose the barrage of questions he could no longer  hold back.


“Oh my god you just walked out of a cloud of smoke there was nothing and then you were all like WOOSH and mysterious and your voice sounds awesome! Are you always like that or can you turn your quirk off?! How far can you warp? Do you have to be able to see it or-”


Kurogiri cut the young child’s energetic ramble off by patting  him on the head.


“Calm down, young one. We  will have plenty of time for questions later. We’re going to get the rest of our group together before we head to your new home. Now, let me help your mother with the rest of your things.”


Nodding quickly, Izuku stepped out of the way as Kurogiri grabbed the last suitcase Inko was struggling to pick up, receiving a relieved “Thank you” from Inko.


With that, Kurogiri opened another portal, and led the pair to the next chapter of their lives.


Tomura Shigaraki sat on the crate, staring across at the... Man? sitting across from him. As tall as a shipping container even while sitting down, he cut an intimidating figure to most people, even while obscured with a cloak and hunched over.


Gigantomachia stared back from his spot, sitting hunched over on the ground but still towering over the small figure, he wasn’t sure what to think of the boy. When Kurogiri came to get him, Machia was excited at the prospect of a job that required him, but being told instead that they were fleeing the country with his master’s heir quickly killed his anticipation. Then being left alone with his master’s… Protege? Left him with a feeling he couldn’t quite describe. It didn’t help that the kid just wouldn’t stop… staring.


He was used to kids gawking at him sure, but this was something different . ‘Empty’ was the only word he could truly use to describe the kids’ stare. . All he was able to gather from Kurogiri was that the kid had been recently taken in by Master, and that his quirk was very destructive. When the portal opened, Machia let his shoulders sag in relief. Finally something got the kid to glance away from him.


When an even smaller figure came literally bouncing out of the rift and looked around in wonder, though, he almost wished to go back to the staring. As Izuku’s eyes landed on Gigantomachia, the goliath saw them widen as they followed his figure from the ground to his covered head. He prepared himself for the imminent scream of fear, but all he got was an awed “So tall...”


Running back over to the portal, Izuku almost made his mother trip as he tugged on her dress to get her attention. Sitting her bags down she picked him up before finally looking where he was pointing excitedly.


“Sweetie calm down! What’s got you wor o o oh my god.”


Gigantomachia let out a snort at hearing her. That’s more in line with what he was used to. As Kurogiri followed Inko out of his portal and it closed behind him, he asked the question that he was fairly sure the answer of.


“This is the mistress and the young master I assume?”


At Kurogiri’s nod, he stood up, rising to his minimum height of 12’ 2’. Before taking a knee, still utterly dwarfing the small woman but making his intent clear.


“Greetings then, my name is Maki Gigan, though your husband tended to call me Gigantomachia. My lord wanted me to guard you and the young master if something were to happen to him.”


Waving her hands in front of herself as best she can with Izuku in her arms, Inko’s fear quickly turned into embarrassment.


“Oh please! You don’t have to bow! Just call me Inko! Please, just call me Inko.”


As Maki rose, Kurogiri made himself known again.


“With introductions out of the way, come along young Tomura, let us all be on our way.”