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As legend has it...

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The seas were violent tonight.

Pitch black, icy cold waves rise from the ocean with a vengeance, washing over the ship's deck and leaving trails of cold wherever it reached with its inky fingers. Nothing was safe from its touch, supplies and people succumbing to its pull over the side of the ship.

The clouds above provided the sea with more ammunition, releasing needle-like drops of rain, icy enough to hurt when one would hit exposed skin. The rain fell so fast from above the sharp edges of the world took on a fuzzy feel, items only a few metres in front becoming a blurry mess.

The wind howled like a wolf during a full moon, forcing the rain to come down at an almost ninety-degree angle. Rain-soaked sails weren't safe from the wind's onslaught, being thrown back and forward and hitting the mast they were tied to with a harsh, wet whap.

That was the last night Katsuki saw his crew.

The sea was a difficult mistress to keep happy and what made her happy that night was the lives of all his crew. It was no real loss for him, his crew weren't all that loyal to him. They didn't trust him and didn't like his temper; they were attracted by the gold. Katsuki was the best at what he did, making him one of the deadliest pirates to sail the seas and one of the richest too; so his crew never went without money, food and women.

Known as The Wrath, Katsuki was legend among pirates who took to the seas. Not a single crew who went against him won the battle. Katsuki and his ship Queen Explosion Murder were undefeated, notoriously fantastic with the aim and power of their cannonballs and other small explosive concoctions his crew threw at their enemies. Sinking every ship he ever came across, the amount of loot on the Queen was immeasurable.

Katsuki's success as The Wrath was admirable and stroked his prideful ego but with a crew he couldn't trust and a dangerous life on the seas he couldn't help but be unhappy.

This isn't where Katsuki wanted to be in life.

The world around him was going through huge changes. Human understanding of the world around them was increasing exponentially with huge discoveries being made in physics and maths. And although modern science, in general, interested him, the emerging science of chemistry was his passion. The understanding of things that could not be seen interacting with one another to create bigger and better things was endlessly fascinating to him.

Katsuki was bright and incredibly tenacious. This landed him an assistant position with the leading chemist in the next town over. He helped run experiments and take notes as to what happened during the reactions. The work was tedious, but he enjoyed it. He was making discoveries and he would help further the world's knowledge.

This is where Katsuki wanted to be. At the forefront of science, obtaining knowledge for generations to come.

However, the master chemist didn't appreciate his attitude. Katsuki was constantly giving advice on how to improve the experiment and bringing in new information others had found but yet the chemist never took Katsuki's suggestions on board, claiming he was too young and dumb to understand what was going on.

Katsuki snapped one day, yelling and screaming at the chemist, all the anger he had held over the course of his apprenticeship rushing over his tongue and through his lips in a torrent of scalding acid.

Katsuki lost his position with the chemist that day.

He moved to another town, another chemist, another old man who didn't want to listen to what he had to say.

Over and over Katsuki found himself with a shorter fuse, quicker to anger at his superiors when they wouldn't give his suggestions the light of day. Soon every chemist in the country knew of him and wouldn't hire him as their assistant. He was well known for the wrong reasons through the science community, even if he was to strike out on his own, no one would take his discoveries seriously.

He didn't belong in the science community.

He ended up in a port town, holding his bag with his mere belongings, looking out to the sea. His white button-down shirt and black slacks were stuck to him, absorbing the cold drizzle that made the port town look more miserable. His ash-blonde spikes were weighed down with water, the usual explosive mess of spikes atop his head gave a valiant fight, but they were droopy, making him look as miserable on the outside as he was on the inside.

His sharp, red eyes took in the town, looking at the boats moored on the dock when a huge ship stole his gaze. Tall and strong the ship looked undeterred by the weather and its inhabitants even more so. They were all in high spirits despite the rain, almost daring it to dampen their spirits. They drank, laughed, sang and stumbled along the deck of the ship.

They seemed to be having the kind of fun Katsuki wanted to be having.

"Ay, before one of ye idiots put yerselves overboard cover the damned gunpowder barrels! We have a hard-enough time lighting the damned bastards without getting it wet."

Katsuki squinted harder though the rain, eyes travelling up the mast to determine what kind of a ship this was when he spies the Jolly Roger sitting limply at the top of the mast, no wind to lift its spirits.

Pirates.

The captain continued to complain about his crew and how he required fresh blood to anyone who would listen. All at the port would lend a kind ear, not wanting to upset the pirate captain lest he decides to turn his crew on them.

Maybe, just maybe Katsuki would belong here.

And so, with the chemistry knowledge he’d gained over the years, Katsuki joined the crew of pirates. Adjusting the ratio of their gunpowder ingredients and changing some ingredients altogether; creating a better, more powerful mix that was less susceptible to water absorption.

This was also the first day he met The Queen, but he didn't know that just yet.

He quickly rose through the ranks, gaining skills and friends as well as a powerful, toned body from all the labour he did on a daily basis, from climbing the rigging to rolling barrels of rum down the deck. Katsuki did it all and learned the ins and outs of the ship very quickly, there was no one who knew her better than he did.

Taking leadership of The Queen when their captain was killed in a raid wasn't met well by the crew and it was only the beginning of his crews’ mutinous ways. They disliked his orders; they disliked his intelligence and they disliked his short temper even more. Which is why when his crew was lost to the mean mistress of the sea, he wasn't all that sad.

His pirating life ended as it began, realising he didn't belong in the world he built himself while the sky mourned its loss.

The sea was restless, already taking his crew and now attempting to take him as well; but Katsuki wasn't letting her take him tonight.

The rain had already plastered his bangs to his forehead, the black bandana he normally wears doing nothing to keep his hair out of his eyes. The short braids of hair behind his right ear were weighed down with beads at their ends and had gotten caught in the fierce winds and were now colliding with each other, adding sharp clacking to the raucous noise that was the storm.

Katsuki wipes his face to attempt to remove some of the rain that had accumulated on his skin and his hand comes back black. The Kohl he has taken to wearing around his eyes has run and has left black streaks down his face. He wipes his hands on his now wet harem pants, creating black smudges on the brown fabric. The thin, tan, cotton V-neck shirt he wore stuck to his form as well, highlighting the muscles he'd accumulated over his time on the ship.

Katsuki was strong-willed and he was going to show the sea that. He steered with all his might, pushing The Queen closer to land, hoping to save himself, but land was nowhere in sight. The rain impeded his sight making it impossible to discern land from deep, inky black seas. The wind howled into the night, adding to the rain pelting the ship's deck and the waves lapping at The Queens sides, creating an orchestra of danger and almost certainly promised death.

But still, through it all, music found Katsuki. Notes so beautiful he felt it in the depths of his very soul. Notes that danced with the rain and made the drops their partners in this sensual tango. Notes that slid down wet slippery masts to waltz across an almost flooded deck to find themselves a home inside of Katsuki's heart.

Katsuki doubled over when the music hit him, almost violent in its impact, surprising him with its beauty. It wasn't just any music. It was the most astonishing singing he'd ever heard, a falsetto so gorgeous it reached into his very body and pulled him in.

The voice sang with no words but Katsuki understood what it was saying.

It just wanted to belong, it wanted to find somewhere for itself in the world. A little piece of the universe that would belong just to the voice. It didn't belong where it thought it would.

He needed to find the source of that voice.

Something inside Katsuki snapped and like a mad man started steering his ship in the direction of the voice, pulling him in and dragging him under its spell. His hands slapped the wet surface of the wooden steering wheel with fervour, causing sharp, stinging pains to shoot through his fingers. His movements became frantic, shaky and desperate, ignoring the pain that was currently travelling though his arms.

Almost as if it was also under the same spell The Queen moved faster than thought possible with a one-man crew, cutting through the dark waves like a knife. The voice was beginning to sound closer, he needed to find it and soon.

The singing continued to wash over Katsuki in warm waves, fighting against the biting cold caused by the storm. The singing so strong and vivid, it's notes almost leave a physical trail above the waves; a beacon beckoning Katsuki towards its source.

Katsuki sees huge rocks rising above him, sharp and rocky cliff faces made soft and fuzzy by the heavy rain still falling from the sky. The sharp spikes of stone reach up from the edge of the sea like a demon would from hell, ready to shred any ship stupid enough to come close. But still the singing implores him to travel further, to sail straight at the rocks in front.

And then he sees him.

The source of the song that danced its way through the drops of rain with practiced ease, not allowing it to dampen its power, only to find themselves buried in Katsuki's brain; driving him insane. The beauty he didn't expect to find splayed across the slippery rocks in the far corner of the world he'd ended up in.

He was ethereal.

Dark green curls, soaked through and bouncing slightly above his shoulder with every note that exited his beautiful, pouty pink lips. A creamy neck, lined with gills that flexed with the effort of singing, exposed when the beauty turned his face towards the sky that paints his face with its tears. The rain darkening the eyelashes that fan across the cherubic cheeks, giving a boyish look to the stranger. Milky white skin freckled with the constellations of the night sky across the bridge of his nose and the tops of his strong shoulders. The small flecks of stardust continue down the strangers strong and toned torso that lead into something Katsuki didn't expect; a tail.

Bright, shiny, emerald green scales began at the end of the stranger’s torso, leading into a long tail that reached into the water. The tail was slim and streamlined for fast swimming, which explained the strong upper body. The tail was a bright emerald where it began, shiny enough to rival the gems themselves, before it transitions into a green so deep it was almost black.

Lightning struck not far from their corner of the world, lighting the seas and the rocks Katsuki continued to sail to, giving Katsuki a glimpse of what the tail would look like during the day. The lightning gave the tail a teal shimmer, each scale dancing with iridescent light. At the end of the tail lay a vee-shaped fin, it was translucent green, tipped in jet black, reminiscent of the dangerous sharks that swam these waters.

But this creature was just as dangerous.

A siren.

But even armed with the knowledge, Katsuki continued to sail towards the rocks. The beautiful being upon the rocks compelling him to sail even faster towards him.

Another lightning strike hits and a roar of thunder tears through the sky, shocking the siren splayed on the stone into silence. Surprised eyes seem to take in their surroundings for the first time, almost surprised that it's storming, before settling on Katsuki's form. The deep green hue of the clearest seas in the Caribbean meet Katsuki's bold carmine orbs before they widen in shock. The siren seems to start moving towards Katsuki, trying to tell him to stop.

The spell of the siren's song has worn off but it's too late, Katsuki has steered The Queen straight into the sharp stones.

The creaking and wailing of wood being torn on the stones is the last thing Katsuki hears before he's plunged into icy black waves. The saltwater stings his eyes but still, the bright, beautiful green eyes of the siren continue to haunt his vision as he sinks into the murky depths of the ocean.

~~~~~~~~~~~~ 

This isn't where Izuku wanted to be in life.

He would often find himself ashore, sitting atop a rock, looking out into the vastness that is the ocean.

He felt like he was born in the wrong skin, too kind and gentle to be a siren, his razor-sharp teeth sitting wrong in his mouth. Eating humans wasn't his ideal, it wasn't who he was. Izuku was endlessly fascinated by humans, finding their trinkets and tools sunken on the bottom of the ocean.

Using his acquired wares Izuku learnt all about the human world through water-logged books and ledgers, understanding more and learning the language known as English. Often Izuku would surface and practice the words on his tongue, fumbling through the noises because of his teeth.

Until one day a man with scraggly black hair and beard was marooned on Izuku's little beach, tied to a floating plank of wood with large, white bandages. The man was stuck there for a while, healing up and resting with Izuku's aid. Izuku would dive into the ocean and bring back small fish and plants for the man to eat. The man had a rough exterior and didn't trust Izuku but after some time he realised Izuku wasn't going to kill him and they began to converse. The man taught him how to speak English properly and fixed his pronunciation, allowing them to converse easily.

Once the man had rested and was well enough to go home Izuku helped swim him to the nearest human town. Izuku dropped him off far enough that no other human would see him, lest they try and kill him. Before he left the man gave him his name, Aizawa, and showed him how to write his siren name in English lettering. Izuku would miss Aizawa, but he was glad to see him return home safely. The man had just barely set foot on dry land when he was crash tackled in the middle of the path by a loud, boisterous blonde. The man was dearly missed it seems.

The man returned to civilization and Izuku to the sea. He continued to swim with his pod, dodging and weaving through plants and caves, but nothing quite excited Izuku as spending time with the human.

But still, seeing Aizawa with the man who obviously loved him tore Izuku up inside, wanting that for himself. Izuku knew his true mate was out there somewhere and that the magic that thrummed through his veins that powered his songs would also bring him to his true mate, shaping them to fit each other.

Izuku knew of his power to attract humans with his voice, singing men to their deaths. He knew songs about loves gained, loves lost and lust, he knew they would all bring men to their watery graves. The songs all hauntingly beautiful and wordless, the magic coming from the feelings the sirens would put into their songs. So Izuku stopped singing about them, stopped putting those feelings into his songs if he sang at all. He didn't want to attract anyone and kill them, he survived just fine on fish and plants thank you very much.

But when Izuku did sing it was beautiful, haunting notes travelling over the waves, painting them with the sorrow he felt about not belonging entirely to his world, not understanding anyone he grew up with.

He sang and sang, and no one came, no one was attracted to his sad song and for that Izuku was grateful.

Izuku escaped his pod for the night and swam to his hidden cove to sit atop his usual rock that looked out to the sea. It had started raining and the clouds above looked fierce. They were dark and looked heavy with rain.

He began to sing, putting all his sadness and melancholy into his notes, letting the storm know just how desperately he wanted to leave his life behind. While he sang, he felt the rain hitting his skin change from fat, warm droplets to sharp, stinging needles that would freeze those not acclimated to living under the sea.

His voice carried across the sea, making the storm raging above him into his own personal orchestra, rain pelting waves kept his beat and howling wind his duet partner. His orchestra arrangement was broken up on occasion by loud peals of thunder but Izuku didn't mind. He could share the stage.

One peal of thunder sounded all too close for Izuku's liking, it's accompanying lightning strike flashing through his tightly closed eyelids, shocking him out of his singing trance and causing him to look around.

He was right the storm was indeed heavier than when he began and his eyes travelled along the coast littered with tall sharp rocks to decide where he was going to dive in a return home. Until he saw something he wishes he didn't.

A gorgeous, tall, blonde pirate was under his spell and was sailing his ship right into the rock underneath Izuku. He seemed to be coming out of it because Izuku has stopped singing but it wasn't going to be fast enough, his ship was travelling too fast and the waves were all too happy to help push the ship along its current course.

Izuku began to yell, to try and tell the man to wake up and turn around but it was too late, his voice was drowned out by the harsh shrieks and moans of the ship as its hull was torn into by the sharp rocks, destroying it quicker than one would think possible.

Before Izuku knew it, the ship was sinking to the bottom of the ocean and the pirate was on his way to an early, watery death. Before Izuku could think he was diving into the ocean, searching for anything that would help him locate the human and bring him to safety.

He pushes through the dark black waves with his tail, thankful he's a fast swimmer as he dodges pieces of the ship that are sinking to the ocean floor. As a siren Izuku's night vision is great, but through all the debris the ship has kicked up off the ocean floor, he can't see the pirate. He's swimming frantically, narrowly avoiding sharp planks of wood, hoping for something that will give away the pirate’s location before it's too late.

As if listening to him the storm creates a huge flash of lightning causing the pirate's pale locks to light up like a beacon, beckoning Izuku down into the murky depths of the ocean. The pirate isn't too far in front of him, slowly floating down towards the seabed. With one last burst of strength, Izuku swims down to pick the pirate up under his armpits and pull him as quickly as possible to the surface, avoiding the sharp rocks at the edge of the cliff.

Izuku pulls the pirate up and drops the man heavily on the flat rock he normally lays on. The impact of his back against the rock causes the man to cough up the seawater he inhaled, covering Izuku's tail in warm but gross seawater. Ignoring what the man did to his tail Izuku lifts his head gently to make sure he doesn't choke on anything else and to have a better look at the man. His eyes looked dazed from the lack of oxygen he just experienced, and his breathing was heavy. With nowhere to put the man now that his ship had sunk, Izuku laid the man's head on his tail and he carded his hands through his wet hair, coaxing the pirate into a well-needed sleep. They'd deal with everything else in the morning.

~~~~~~~~~~~~ 

Katsuki wakes to a warmth he hasn't known for a while, the ship's quarters always freezing from the icy waters that lay underneath them. He cracks open his eyes to see the cloudless sky above, washing him in sunlight and making it hard to see. Slowly coming to he realises he's resting on a hard rock, but his head is pillowed on something fleshy. He turns his head to the side to see a large green tail wrapping around his side, keeping him warm. He follows the length of the tail, leading up to its thickest part where his head was placed. He turns to his other side to see a human torso. The man’s eyes closed, breath heavy and his green curls springy and messy atop his head. With every heavy breath flaps of skin on his neck would flutter, as if caught in the flow of air through his lungs.

The siren.

Why was he asleep on the siren that lured him in last night? Why hasn’t it eaten him? And more importantly, why wasn’t he dead?

The last thing Katsuki remembers is sinking to the ocean floor, the siren song entrancing him and causing him to sail straight into the sharp rocks at the bottom of the cliff.

He gently lifts his head from the siren’s tail, creeping away as slowly as possible so as to not disturb the sleeping man. He stands up on shaky legs and looks around him. The sea stretched endlessly in every direction and behind him a steep wall of sharp rocks.

He plops himself down onto the wet rock, sitting and facing the still sleeping siren. Katsuki waded through his muddled memories of the night before, remembering the siren’s beautiful voice and the way it beckoned him closer before it gave way to the siren’s surprise and worry when it locked eyes with Katsuki.

Why would a siren try and stop him from sailing into the rocks and to his death? Why would it save him? He was as good as dead.

Across from him, the siren begins to stir, stretching his arms and curling his long tail before sitting up quickly as if electrocuted.

“Oh no, oh no, oh nooooo, ohnoohnoohnonononono. I fell asleep on land! Everyone is going to kill me! And my tail has begun to dry out. Humph, that will teach me.”

The siren speaks English, although heavily accented, with words slipping strangely over and around sharp teeth. This was surreal.

The siren looks poised to jump into the ocean below when he turns and spots Katsuki sitting on the rock, staring at him. Surprised to see Katsuki there the siren messes up his ocean re-entry, hitting the water stomach first, the action creating a large and painful sounding splash. The siren resurfaces quickly, his entire torso painted in an angry red from his far from graceful bellyflop into the ocean and stares intently at Katsuki.

“A human?”

“Yeah, I’m a human, you dumbass, did you forget everything that happened last night?”

“No... Uh... ok, maybe I did? I just... I was in a rush I guess, sorry.” The siren replies, scratching at his now wet curls.

The siren continues to stare, scrutinizing him, almost as if checking that he was, in fact, telling the truth about his human status.

“So I guess I owe you thanks for my life I guess. Even if you were the reason I almost died to begin with.”

The siren’s face fell at that, gaze trained into the depths of the ocean making Katsuki feel bad. He was only half telling the truth. If he hadn’t followed the siren’s voice to this rocky island he would have perished in the storm, instead, he was here; alive and with a very strange siren who didn’t eat people.

Katsuki opens his mouth to apologise, not being able to handle the sadness in the sirens face when it speaks up.

“Yes, I’m very sorry about that. It’s just that... I need to sing, it’s in my nature, but I don’t like luring humans. I don’t really belong in my world so I sing about it. And not once. Not once did anyone come, lured in by my song. Why you?”

The siren’s steely gaze is now focused on Katsuki, his face betraying his confusion at the situation and the almost painful need to know Katsuki’s answer.

Katsuki turns away, the gaze too piercing, too searching and to genuine for him to handle. It’s been a long time since he was shown anything but contempt. Contempt from those who knew he was a pirate. Contempt from those who thought he was too brash to understand chemistry. Contempt those he spent most of his days and nights with, a family on the sea, who didn’t care for him either, quick to jump ship.

“I never really belonged anywhere either...”

The siren lets out a small, wordless whimper at the heartbroken tone of Katsuki’s voice, eyes filling with tears. He quickly disappears under the water only to resurface on the side of the rock, slowly pulling himself up to sit beside Katsuki.

The siren looked at a loss for words, hands wringing each other nervously before they would stop briefly, start to reach out to Katsuki before they stopped and went back to their nervous ways.

“I... I- ah, I’m sorry.”

“It's ok. It’s not like you did this, plus you obviously understand, you don’t feel like you belong where you’re supposed to either.”

“You’re right, I don’t belong. It’s one of the reasons I saved you last night. I don’t want to kill humans. I don’t want to eat you, your culture is so fascinating and all the knowledge you guys have. I mean last I heard you guys are starting a new thing called science! You’re learning how everything works around you and that’s amazing. Why would I want to kill someone like you for no other reason than I can? That’s why the other siren’s do it. Because they can. We can live on fish when we can’t lure in humans so why bother doing it all together?!”

“Wow, you sure have some strong views on hunting humans. But did you are you’re interested in science? That’s the last thing I expected to hear.”

“Yeah! You guys have made a lot of advancements between the time I read a book I found on a shipwreck to the time I saved the other human! He taught me so much.”

“That explains why your English is so decent.”

The siren hums in wordless agreement to the statement, nodding his head.

“Ok then, seeing as you’re a siren with a thirst for knowledge how about as a trade for saving my life I teach you everything I know about science?”

“You would!”

“Yeah, I don’t like owing anyone anything and before I was a pirate I studied a science called chemistry. It’s up and coming at the moment and it’s the study of the composition of the world, explaining why things do what they do on something called the atomic scale. That’s a plane of existence so small we can’t see it with the human eye.”

“Woah! That’s so cool, tell me everything... Ah sorry, what are you called?”

Katsuki smothers a snort, the siren is adorable, his head tilted as he looks up at Katsuki, head tilted in question like a puppy.

“Name’s Katsuki, what about you?”

“Kasthu- ka... Katchukee... Katchu... Kacchan? Kacchan! My name is Izuku.”

Katsuki sat there dumbfounded, the siren can speak almost perfect English but it can’t pronounce his name through his sharp teeth and heavy accent. Well, he’s not the only one who can come up with new names.

“Deku is it? A very fitting name for a siren that doesn’t behave like a siren. Heard some Japanese fishermen calling their rookie that. Apparently means useless.”

“That’s mean Kacchan.” Izuku crossing his arms across his chest and pouting.

“Well then settle in and prepare for me to drop some knowledge on you cause if you’re gonna be useless as a siren at least you can be useful as a scientist.”

“Okay, Kacchan! Teach me your ways.”

“Well the word atom actually comes from Leucippus and Democritus, two philosophers in ancient Greece, they came up with the word, hypothesising that at one point if we keep making things smaller by cutting them there would be a point where you couldn’t cut them anymore. Atom is derived from atomos, which means indivisible...”

The two sat atop the rock, one listening intently as words pour out of the other’s mouth like a violent torrent, washing away all questions that lay in its path. Every nook and cranny that was previously filled with a burning curiosity for the world was now filled and sated with the spoils of knowledge the pirate had for the siren.

“Amazing, the world is so amazing!”

“You’re a curious little siren aren’cha. You’d make a fantastic scientist, that’s the main thing you need. Curiosity.”

“Kacchan is amazing! He knows so much! He’s so smart!”

This causes the pirate to blush, bright red appearing from the apples of his cheeks to trail over the tips of his ears.

“It’s no big deal,” Katsuki mumbled under his breath in embarrassment. He wasn’t used to receiving praise from anyone, especially about his scientific knowledge.

“Yes, it is! You taught me so much about the world today! Thank you so much!” the siren exclaimed excitedly, a blinding smile stretching across his face before it slowly soured and fell, eyes downcast and gaze settled on the rock they sat on.

“Hey,” Katsuki says, slowly moving into the siren’s space, “what’s wrong?”

“I enjoyed learning so much today, and I’m grateful for it, but Kacchan is amazing and one of my only friends, I’m going to be sad to leave him in the human village this afternoon and never see him again.”

Katsuki thought on what the siren said, he was right, they’d only spent a short time together but they had such a great time together. It was like they had known each other forever and they’d become quick friends. Katsuki didn’t want to leave, but he couldn’t spend the night on this rock,

“Hey, it’s ok. You can drop me off at the human village so I can get a good nights rest and heal up from my near-death experience yesterday and then I will come down to the beach to meet you so we can hang out.”

“Really? You’d do that!”

“Yes of course,” Katsuki scoffed,” I don’t say anything I don’t mean. Now let's get going, I’m sure everyone was wondering where you got to.”

The siren jumps back into the water, albeit more gracefully, and pops up in front of Katsuki.

“Get in Kacchan! The water is lovely!” the siren says before twisting sharply and splashing Katsuki with his tail, sending a mini tidal wave over the rock and into Katsuki’s face, causing him to inhale some of the seawater.

“Oi! You little shit!” Katsuki screams in-between coughs as he violently evacuates seawater from his lungs, “You’re gonna regret that!”

Katsuki jumps in right on top of Deku, aiming to drag the siren underwater with him, completely forgetting sirens are a creature of the deep. Izuku floats underwater in Katsuki’s grasp, a mocking smile stretches across his face as the gills on his neck flutter and release bubbles of laughter. Izuku grabs Katsuki by the waist, entwining their arms and pulls him up to the surface.

“Fuck you!”

“Don’t be so salty Kacchan leave that to the sea.”

The siren grabs Katsuki and puts him on his back, making for one very wet, very slippery piggyback.

“Come on let’s get you to the human town.”

Katsuki would be happier about having a better place to sleep for the night if not for the melancholy tingeing Izuku’s voice. He really didn’t want to leave the siren.

The swim was quiet, no words spoken between the two as they cut through the dark waves, Izuku’s strong tail making the swim smooth and graceful.

All too soon for Katsuki’s liking the pair arrive at a cove, not far from the human town but far enough no one would see them arrive or leave.

Katsuki slides off Izuku’s back and plops into the now shallow water, his body shivering from the cold that suddenly rushed over him. If it was from the sea sapping his heat or if it was the lack of contact with Izuku he couldn’t tell you, but leaving was the last thing on his mind right now.

“So, this is it.”

“Yeah, it is... Safe travels to wherever your kind lives or whatever.”

“Thanks, Kacchan. I hope you have a good sleep.”

The conversation ended in sad silence, neither of them wanting to leave the other, their eyes looking at everything but each other, as if making eye contact would remind the other they had to leave.

“I’ll miss you while you’re gone Kacchan.”

“It’s ok, I’ll be back here tomorrow morning. Bright and early. Don’t get your nerd ass lost on the way.”

The siren sent Katsuki one more blinding smile at that, before diving into the water and disappearing from sight. With a huff, Katsuki heaves himself out of the water to try and dry out on the land before finding a place to stay for the night, but for some reason being away from the water wasn’t somewhere he wanted to be.

~~~~~~~~~~~~

Izuku swam home on a high, excited to have learnt so much about the world above him and have his understanding expanded. But most importantly he was glad to have made friends with Kacchan, the pirate was so smart and knew so much! He was gruff and had a rough exterior but he had a soft heart inside. Izuku was lucky to have seen it.

The closer he got to his home the more anxious he became. He was concerned about what his pod would think of him, being gone for so long. Hopefully, he didn’t concern anyone and they didn’t think he was dead!

Izuku started ducking and weaving through familiar rock formations, his siren pod secretive and hidden. Humans tried to hunt them to extinction to prevent them from killing their loved ones, so in return, the sirens hid in a part of the ocean so deep that no human would ever dare to traverse. But perhaps now with their newfound scientific knowledge, the humans might have an upper hand and the sirens could be facing death.

Izuku finally made it into the little plateau on the seabed. The area was open and spread as far as Izuku could see, bordered by high rocks on every side to make it more difficult for predators to get to them. The place was reminiscent of a human town. A market place on one side where some sirens made their livelihood trading their wares found when scavenging shipwrecks and on the other the school where they all learnt how to use their magic when singing their songs. Heading straight across the plateau, Izuku swam towards the other end of the city where all the caves were. Each family of sirens had their own cave to call home, not that it felt that way to Izuku. His mother died some years ago leaving him alone and lonely. No one else in his pod understood him or even tried to. He’d made a few friends, but other than running into them on occasion they didn’t really see each other often.

Swimming through the dense throng of sirens heading to their own caves Izuku searched for a familiar face when he recognizes his friend Ochako. She was great friends with Izuku when he was younger, going to school together and learning the ways of their kind. They had drifted apart when they were older, Izuku realising his admiration for the males of his species was a sexual attraction and that he wasn’t interested in mating a female.

So when Ochako confessed her feelings for him he was surprised because not only had he expressed to her his interest in men but the eons-old magic that thrummed through all siren’s veins and gave them the magic of their songs also helped them find mates. Their bodies knew who their mates were and they were inexplicably drawn to them and his body told him otherwise, Ochako wasn’t for him. Ochako had a mate just like he did, they may not be in this pod but they were out there. He turned her down as gently as possible, telling her that she’d find her mate and that this crush would pass. She was livid, screaming about not being a slave to magic and having it set their destiny. Their friendship didn’t survive the fight, straining it beyond repair and now the two barely spoke, but still, Izuku would go as far as to call them friends.

“Ochako! Hey, I’m back! Sorry if I worried you.”

“Oh, Izuku! You were gone?”

“Uh... Yeah, for two whole days?”

“Oh, I didn’t notice.”

“Oh, haha, never mind then I guess… I’ll see you around?”

With a strained smile that betrayed how little she cared for Izuku, Ochako turns her back on him and swims to her friends who were watching the whole thing and we’re now laughing at him with malice. Whispers of 'he was gone?’, 'what a weirdo', ‘why would we notice?’ and ‘he should have stayed gone' reach Izuku’s ears, breaking his heart.

No one noticed he was gone.

Not even his friend.

No one.

And they wished he didn’t come back.

Izuku swam into his cave, diving into his messy nest, beginning to cry. Tears welling up in his eyes, making them glassy, before they fell, only to be swept into the sea, adding to the saltiness of the water.  Izuku didn’t know what to do, he didn’t want to be here, he had never belonged, so why was he still living here?

He fell into a restless sleep, exhausted from all the crying.

When he woke he could feel his eyes were still swollen from the tears he wasted on people who didn’t deserve them. So he gets up and steels himself for what was to come.

He was leaving.

He’d decided he was going to live near the human town, taking care of humans who might drown and in turn getting knowledge from them. But first, he was going to meet with Katsuki again. Thinking about the blonde was like an electric bolt travelling down his spine, ending in his stomach, leaving butterflies there and zapping him into action, having him work faster than before. Seeing the pirate was a great incentive.

Izuku packed his meagre belongings into a hemp bag he found at the bottom of the sea and started to swim out of the plateau for the last time. He’d heard stories of sirens striking out on their own to live alone before and he was going to do it for himself. He was going to be lonely and mateless, but at least he’d have the knowledge to sate him and be close to the human world that fascinated him so much. And truly that was where he belonged.

Izuku swam back through the familiar paths and rock formations he came through yesterday, committing his childhood home to his memory before leaving it behind forever. He has many happy memories here when he was young with his mother. If she could only see him now, would she be proud? Tears begin to fall from his face again, thinking about how he’d never get to see her again and never live in the home they both grew up in. He was leaving behind all his history.

As soon as he leaves the immediate vicinity of his town Izuku swims with one thing in mind, seeing Katsuki again. He wipes the tears still in his eyes and swims faster and with a purpose. He reaches the beach he left Katsuki at in record time and surfaces, coming face to face with the man that has been haunting his thoughts ever since he saved him. Katsuki’s eyes travel over Izuku, drinking in the sight with an almost fond look on his face as if he’d missed him. As if he was a vision from a dream. If he noticed his eyes were swollen and his cheeks a splotchy red from crying, he didn’t say anything about it.

“About time, I thought you weren’t coming. I’ve been here for hours.” the pirate laments.

“Sorry, Kacchan! I didn’t realise you’d be here so early!”

“Tch.” Katsuki turns, trying to hide the blush that was now spreading up from his cheeks. The man was embarrassed to be waiting on Izuku, embarrassed he missed the siren’s company.

The pirate had taken off his boots, letting his now bare feet dangle in the sea, kicking up little splashes into Izuku’s face.

“So, we had a deal. Tell me about your life.”

The entire day was spent with the two sharing only each other’s company, again with one completely enthralled with what the other was saying. Izuku was having a great time explaining about his past, he never thought he’d find someone so interested in his life, talking to him about what he did under the sea, how his world worked, what it was like where he lived. It was a breath of fresh air.

The sun began to reach the ocean, kissing it gently as it only had a chance to do so twice a day, not taking its an opportunity for granted. The horizon begins to swallow up all light that covered the world. The slow crawl of dark shadows across the cove slowly removed the gold glow from Katsuki’s blonde hair, alerting Izuku as to how much time they had spent together.

“Wow, we didn’t even have lunch,” Izuku said, sentence punctuated by a loud grumble from his stomach.

“Yeah, it's ok though, I didn’t even notice.” The pirate moved his gaze from the siren in front of him to the horizon, a soft look crossing his face. Izuku had never seen him look so young and carefree, he’d been plagued with worries since they’d met.

“Tomorrow I’ll eat a big breakfast so I don’t have to worry about lunch and then a big dinner.”

“Why? We can just have a short break for lunch?”

“Nah, I really don’t want you to leave, if only you could join me for lunch in a pub or I could join you for some fish.”

“That would be amazing Kacchan…” Izuku whispered, imagining how amazing it would be if he and Katsuki were of the same species, the fun he’d have on land learning about chemistry. The fun Katsuki would have underwater diving through shipwrecks.

“Well, the sun is setting and I don’t want you to run into trouble as you head back to the inn, I’ll see you tomorrow Kacchan!”

“Bye nerd.”

With a quick wave, siren turns and heads into the water, his heart hurting more the further he swam from Katsuki and closer to his lonely new nest. Not that it’s far from the beach, not wanting to be too far from the pirate, his heart hurting just to think about it.

~~~~~~~~~~~~

Katsuki didn’t want Izuku to leave, he was so far away in the ocean, his heart clenched painfully every time he left, he could almost feel every kilometre away he swam. He wished more than anything that he was born of the same species so he could spend his days swimming through the ocean and discovering all the things Izuku spoke about. The beautiful rainbow fish among the equally colourful reefs, getting up close and personal with majestic whales and dangerous sharks. The gracefulness of swimming through rocks and tunnels, discovering caves filled with bioluminescent algae, giving the sea an ethereal blue glow. The algae washing a pale, freckled face in blue light. Green eyes glowing a stunning teal, the blue light shimmering off a green tail, scattering turquoise light on the walls.

Katsuki wished he was born as a siren.

Every step away from the sea was painful as if the water had claimed him as one of its own, embedding itself into his soul. But he knew that’s not what his soul actually belonged to. His soul was Izuku’s, now irrevocably intertwined. He could feel it. Over such a short time he’d become close with the siren, he didn’t want to leave his side.

God, he couldn’t believe himself. He was The Wrath of the sea, one of the most feared pirates. Why was he now missing a little green-haired siren and his company? How had he become attached so fast and most importantly; why couldn’t he live without Izuku anymore?

The next morning he woke up early, the sun hitting him directly in the face as if his mere existence upset it. He rolls out of bed, lethargic as he drags himself downstairs to have breakfast at the inn. His sleep was restless, the distance between the sea and his bed in the inn a physical weight on his chest, making it almost impossible to sleep.  

He makes sure to get the biggest meal possible, ensuring he would stay full until dinner. His heart could not bear the thought of being away from Izuku for longer than it had to be. And while that was a concerning thought in itself, with how quickly he’d become attached to the siren, the thought of seeing Izuku for as long as possible lightened his soul.

Katsuki finishes his breakfast at record speeds and heads out to the little beach that had inadvertently become theirs. Kicking his boots off into the sand, he sits and sticks his feet into the cool, soothing water. He moves his feet back and forth under the water, causing ripples to appear on its surface. The water that lapping over his calves, leaving an icy touch over his skin that he missed. The way Katsuki felt about the natural chill the sea had changed. He no longer feared its icy fingers tracing over his arms like he had the night he had almost drowned with his ship. He now welcomed the chill, soothing an itch that almost permanently lived under his skin when he was away from the sea and ultimately Izuku.

He waited patiently for Izuku, he wasn’t to know about his itch to be in the sea, forcing him out to their beach early in the morning. Hopefully, he would arrive soon though, he really enjoyed the sirens company. Katsuki continued to tread the water with his feet, kicking them slowly though the gentle waves when he looks down at his legs. In a few places, there seems to be patches of shiny orange skin, glittering in the water on his leg. Moving his legs shifted the angle the light hit the orange skin, giving the orange an iridescent red shift, making its glow ethereal.

Katsuki was taken aback, they weren’t there this morning. He reaches down to touch them when they disappear as suddenly as they appeared, the orange scales morphing back into skin. He’d heard of strange hexes and spells being put on unsuspecting victims; their world built on old magic that no one knew about. He hasn’t been doing much but spending time with Izuku lately so it was unlikely he’s angered an ages-old spirit.

Katsuki reaches down into the water and when his hand does meet his leg, he runs it over the skin to find nothing strange. Just as he’s about to remove his hand from the water he notices a shiny orange scale on the seafloor. He picks it up and moves it in the light, having it dance off its shiny surface and provide an iridescent red glow. He’s enamoured by the scale, maybe another siren lost it while swimming. Thinking nothing of it Katsuki pocketed the scale and continued to wait for Izuku to arrive.

~~~~~~~~~~~~

Izuku had the worst sleep. He felt so far from Katsuki and the land even though he was only a few kilometres offshore in his nest. The nest’s location was as far as he could possibly bear from the land and Katsuki. He had no idea why, but he and Katsuki had inexplicably bonded this quickly, their very souls intertwining with one another before they’d even known it. It was as if they were each other’s complement in every way.

With that thought Izuku headed off to their little beach, eating as many fish he could hold on the way so as to not waste any of the moments he could spend with Katsuki. On approach he finds bare feet kicking back and forth in the ocean again, Katsuki no doubt. Swimming up to the man he pops his head up above water just in front of the feet and shakes the water out of his eyes, splashing Katsuki.

“Oi Deku, what the fuck.”

“Haha sorry, thought you wouldn’t mind a bit of seawater seeing as you’re a pirate. Didn’t realise you’re so precious.”

“Hmmph, don’t go making assumptions, I’m one of the best pirates around!”

That made Izuku pause, saddened by the fact that it was his fault Katsuki could not longer pirate, inadvertently being the cause for it’s sinking.

“Oi, don’t get all mopey on me,” Katsuki begins, reaching over to Izuku’s face and smoothing out the wrinkles that had appeared between his eyebrows with his thumb, “sadness doesn’t look good on you.”

“I’m sorry Kacchan, I just feel bad cause now you can’t be the best pirate.”

“Don’t be, the Queen was destined to sink that night and if it wasn’t for you luring me in I would have sunk with her. The sea is unforgiving... unlike you.”

Izuku cracked a smile at that, swimming in closer so he can perch himself near Katsuki.

“So, tell me what it’s like to be a pirate.”

The day went too fast for the pair's liking, the sun setting on the horizon much too soon and painting the world in deep golds and purples, shadows stretching further across the land. Stomachs complained about their lack of contents but still, the pair didn’t want to separate. The day full of tales about Katsuki’s adventures on the high seas and his prowess with gunpowder from his chemistry background. The tales were exhilarating, it felt almost as if Izuku was there and lived them. The Queen Explosion Murder had her name for a reason, Izuku learnt, and no other ship would be her demise, it was fitting only something as strong as the sea would be the one to take her.

When there was no more gold amongst the world and the purples had transitioned into black the pair decided it would be safer to leave their beach and go to sleep, the parting painful and unwanted by both. Only the promise made under the stars that they would see each other again tomorrow is what kept them going.

Watching until Katsuki’s blonde spikes were out of sight, Izuku dives back underwater and towards his nest. How he wished Katsuki could join him in his nest down on the ocean floor or he could share Katsuki’s bed with him on land. That thought gave Izuku pause, these last few days they’d spent together were great, bonding quickly and becoming quick friends. But for the feelings to become those one would share with a mate, it was ridiculous. Sirens always mated quickly, the small amount of magic left in thrumming through their veins allowing them to fall in love with their fated. Legends say this is so the sirens become more powerful, their songs strengthening once a siren is mated, almost as if sirens evolved this way for their survival.

Izuku was astounded, he’d never found anyone his body wanted, had never found his true mate, and for his body to designate a human as his mate; he wasn’t quite sure what to do about it.

Swimming further to the bottom of the ocean, considering what to do with his newfound information Izuku suddenly realised he was having a great difficulty swimming and that suddenly he could no longer breathe. Hands frantically coming up to his neck where his gills would lay he found nothing but smooth skin. This caused Izuku to panic and twist under that water violently, turning to see that his torso no longer ended in shiny green scales but two long, pale legs. The legs were not as powerful as his tail, his new feet not able to cut through the water as his fins could. He was so deep underwater and his body was no longer equipped to exist here, the pressure starting to give him a headache, so he tries to swim to the surface. His lungs were burning with the effort his body was putting in and from the panic that had settled deep into his bones.

His new legs gave a valiant effort but still, the surface was so far up he wasn’t sure he was going to make it. Faster and faster, harder and harder he pushed his legs, anything to not give up so he can reach the surface, his body burning with the effort it took until black started to creep in along the edges of his vision. He was losing strength and the lack of oxygen was going to make his pass out.

He was going to die.

He’d never get to see Katsuki again, the mate the fates had destined for him. Never get to hear his deep chuckle, hear more about the land and about science, never hear about his pirating stories again. Izuku would find his mate only to have him torn from his clutches. It made a lot more sense as to why he didn’t want to leave Katsuki when the time came, why their distance was physically painful.

The black continued to take his vision and the surface started to get further from his grasp as his new body succumbed to the sea, the lack of oxygen causing his muscles to seize.

As his body slowly sunk to the ocean floor, tears began to fall from his eyes only to be washed away by the sea. The tears for a love only recently gained and so quickly and cruelly lost. Maybe that’s why he became human, the magic that designated Katsuki his mate making it possible for them to be together. It struck at an unfortunate time.

Just as that realisation hit Izuku his vision cleared, no more was he slowly drowning, the water becoming his source of oxygen once more. Touching his neck he finds his gills have returned and looking down he sees the green of his tail. Crying out in joy he heads to his nest to sleep, he needs to rest up from the harrowing experience he just had and be ready for his meeting with Katsuki tomorrow. It’s time he knows about his feelings.

~~~~~~~~~~~~

Katsuki has the worst sleep ever. He’s constantly twisting and turning, unable to find a comfortable position to sleep in. Every time he tries to get comfortable an itch makes it’s way under his skin and irritates him.

The itch is insatiable.

Its as if his body is craving something and it won’t settle until he has it. He has an idea on what his body craves because when he finally falls into a fitful sleep he dreams of wide-open seas, clear skies and gentle waves that come and lap at sand-covered feet. The sting of the salt on the wind burns his eyes but still, he looks to the sea, only to see Izuku swimming through the waves leisurely. Izuku spots him on the beach and waves, beckoning Katsuki into the deep blue sea.

Katsuki wastes no time getting into the sea, wading in before the water is deep enough for him to swim in. He swims and swims, putting more effort into his strokes in an attempt to reach Izuku faster only to see he’s gaining no ground on the siren’s location. In anger he starts to give up, energy sapped and motivation lost.

He would never see the siren again.

He succumbs to the waves only to find he’s not drowning and he is making significant progress towards the iridescent green tail he can see under the water.

Katsuki looks down his own body to see he’s topless and that his torso now ends in a magnificent deep orange tail, the same deep orange of the scale he found in the rock pool. The orange catches the light, causing it to glow gold in the dark waters he’s traversing. The tail slowly transitions into a deep black at the bottom, a flared betta fish like fin at the base of his tail. The fin was edged in deep orange, the fin reminiscent of the explosions he used to cause as a pirate. Two smaller matching fins adorned the sides of his tail halfway down, giving his tail a dangerous look. He felt like one of the poisonous fish that scared the others off with its colouring. The tail felt so right.

Katsuki took the tail in his stride and continued to swim towards Izuku, faster smoother than ever. He finally reached Izuku, grabbing the siren by the waist and pulling him into a fierce kiss, sharp teeth clicking and mouths sliding over one another sensually. He moved his arms from Izuku’s waist to tangle them in his hair, not breaking the kiss once, while Izuku took to rubbing Katsuki’s broad shoulders.

Katsuki pulled back to stare deeply into Izuku’s eyes, their deep green sparkling with mystery.

“Deku,” slurred Katsuki, his new sharp teeth giving him grief with his words.

“Kacchan,” Izuku replied, pulling Katsuki closer and running his hands reverently across his back and chest. Tails begin to twist together, bodies twirling around one another in a dance as faces are drawn to one another like magnets.

As their lips brush over each other again Katsuki comes to, breathing heavily in the uncomfortable bed he rented at the inn. The dream was so real he could feel his tail, the way the water moved around him while he swam as if his mere presence caused it to bow out of his way, almost as if afraid of him. But most importantly he could feel Izuku, his body pressed flush against him in the surf, warm kisses shared in the chilly depths.

He’d fallen for the siren.

Katsuki makes to get up and head to the beach, excited to see Izuku again but also afraid to tell him of his feelings, when he realises his legs are no longer there. He takes the blanket off to see the tail from his dreams is real. The deep orange dulled by the morning light and the black fin at the end of his tail fanned out over the bedsheets, the white backdrop making the orange edging on the fin even brighter.

Katsuki panics, how is he going to reach Izuku like this, how is he going to reach the sea like this? He needs to be in the sea to see Izuku, he needs to spend the rest of his days with the siren. He needs to spend the rest of his days in this body.

He tries to flop out of bed in his haste to see Deku, only to think about just what he’s doing. Sirens are feared and hunted, showing up and flopping his way downstairs was a sure-fire way to get himself killed. He stops his endeavour to get himself out of the bed and thinks about his next step. He needed to get out, but how?

He takes a deep breath in, the salt from the sea making it’s way into his lungs as it’s carried on the air. The saltines carries with it memories of Deku from the short time they’ve known each other. There must be a magical element to their bond from the siren’s magic, drawing them all the more closer to each other. Breathing out he opens his eyes, mind still wandering through memories bright green eyes and tinkling laughter. The memories send a zing through his body, setting all his nerves on edge and leaving goosebumps in their wake.

He was a fool, but a fool for Izuku.

He prepares himself again to try and get out of the bed when he looks down and sees his legs have returned, with the addition of a few patches of bright orange scales. He reaches down and passes his hands over his legs to ensure they’re actually there when he comes to the edge of one patch of scales. Running his hand around the sharp edges and then onto the smooth top. The scales were cool under his fingertips, the natural curve of each one giving the patch a bumpy texture.

He had to show Izuku.

He gets up and dresses hastily before almost tearing the door to the inn off its hinges. No one was getting in-between him and Izuku. Not even breakfast.

Katsuki runs to the cove, pushing through crowds and forcing people out of his way. Each step closer to the sea the faster he moved and the more violent his legs shook. Unbeknownst to him, Katsuki’s violent steps forced the scales to detach from his legs, falling to the stone floor with a soft tinkle.

He reaches the ocean and looks down, seeing the orange scales had gone. He panics, thinking there’s no way he can prove to Izuku now that he had a tail.

“Fuck!” he screams into the empty beach, the rocks around him causing his anger to echo back at him and dance around the beach.

Sadly he removes his boots and sticks his feet into the sea again, feeling the cool water lap up his thighs as he waits for Izuku. He has missed him in the time he’s been away from the beach, his heart feeling better now that his feet were in the sea and he was substantially closer to Izuku.

Izuku, the love of his life, he realises with a start.

He wasn’t left waiting long for the siren, a mop of dark green hair popping up from the ocean just to his left and slowly heading over to where Katsuki was sitting.

“Deku.”

“Kacchan! You’re here!”

“I wouldn’t be anywhere else nerd. Nowhere else.”

The fond tone in Katsuki’s voice causes a slow, warm smile to stretch across Izuku’s face. The siren swims closer, reaching a hand out slowly to run it reverently over Katsuki’s legs. Katsuki struggles to repress an involuntary shiver, the touch feeling so good. Everywhere Izuku touched orange scales sprout up, covering his leg and giving them an ethereal glow yet again.

“So it’s true,” Izuku breathes out quietly, “You’re my mate.”

“Yes.”

Katsuki quickly strips off his clothes and puts them next to his boots, sliding into the water next to Izuku and joining him in the surf. Swimming over towards the siren slowly and reaching out with his arms.

“You told me about how mates work in your kind, you never said anything about how it would work if I was human.”

“Our magic is never wrong; it knows who is right for us and will adjust accordingly.”

Izuku punctuates that sentence by diving into the water and beaching himself, staring at Katsuki as the deep iridescent green of his tail disappears and gives way to milky white skin, dotted with freckles like his torso. Katsuki’s gaze travels up Izuku’s newly formed feet and across strong, toned thighs and up higher to a tight perky ass. Katsuki quickly looks away, flushing red when he realises just how gorgeous the siren is in human form as well, not letting his mind wander back to what he saw sitting between the siren’s thighs.

“You look beautiful, Katsuki.” The siren’s human form gave him blunt teeth, making it easy to move his tongue through the motions of his given name. Katsuki feels the heat of Izuku using his given name through his body, clouding his mind making him process what the siren said slowly.

It finally clicked that the siren was staring at his legs, or where they should have been. His tail was back in all its glory, from the deep orange of his scales that lead into his orange-tipped black tail fan at the base. Katsuki let a big smile cross his face as he dives back into the water and begins to swim through the ocean. This is what his body has been craving, this is what he’s wanted since meeting Izuku. He’s missed the sea. He’s missed the siren.

Katsuki surfaces and looks into Izuku’s eyes, who is staring at him with such love and intensity it causes him to blush.

“Are you gonna join me Izuku?” the question sits heavy in his mouth, struggling to make its way through his new sharp teeth.

“Yes... This is what I’ve wanted since I’ve met you Kacchan, I’ve wanted you to experience my world and I’ve wanted to experience yours.”

Izuku slips into the ocean and when he resurfaces his gills have returned on his neck and his legs swapped out for his strong tail, brushing it sensually against Katsuki’s.

Katsuki begins to lean into Izuku, grabbing the siren by his waist and pulling him into his body, their faces beginning to close in on each other, breaths mingling in the space between them.

Before their lips can meet Izuku puts a hand on the middle of Katsuki’s chest, pushing him back. Katsuki is confused and it shows on his face, about to ask what’s up when Izuku twirls his tail with Katsuki’s sensually.

“I’m sorry Kacchan, I need to let you know that once we kiss, I’ve claimed you as mine and you’ve claimed me as yours. We become mates. It’s how our magic works.”

Instead of saying anything Katsuki just takes Izuku’s face in his hands and brings his lips up, pressing a tender kiss to his lips. Trying to convey just how much he’d come to love the siren over such a short amount of time. To show just how thankful he was to have met him and grateful he was that the fates determined that Izuku was his mate.

With the kiss that seals the relationship for years to comes a faint thrum of magic passes over them and leaks out into the ocean, giving the water near them a faint gold glow to it. They pull back and they’re both shrouded in a golden light that seems to emanate within, the light bouncing off the surface of the water around them, colouring the rest of the world in golden tones.

The gold light starts to recede, the golden halo of light around them slowly shrinking and moving down their body until it concentrates around their left hands and then with a bright flash leaves matching golden tattooed lines winding up their fingers, over the back of their hands and through to their wrists. The tattoos looked like twisted ropes from the rigging of a pirate ship, curved and bent like the edge of a wave.

A perfect amalgamation of both their worlds. The tattoos bound them to one another for life and they wouldn’t have it any other way.

The magic slowly dissipates from the tattoos, leaving stark black lines across their hands. Izuku reaches to pick up something from the seafloor and returns with wet hemp rope from the floor.

He takes Katsuki’s left hand with his own and with his other begins to wrap the rope around their hands.

Izuku looks up to meet his eyes, “I got this from the Queen Explosion, I visited her yesterday, we can make our nest there and it can be our home, remembering the ship you called home. We can pay homage to our destined meeting and pay thanks to the fates this way.”

Izuku looks down at what he’s doing and continues to wrap their hands in an intricate pattern. Around their wrists, down through their fingers and up through the other side of their hands.

“With this binding, I make us one. One in mind, one in body and one in soul. You are my partner, my lover, my mate. From this day on I will thank the fates for bringing you to me on that stormy night but most importantly I thank the fates for allowing you to be a siren with me in the sea and for allowing me to be a human with you on land. With this, I claim you as mine.”

Izuku never said he had to join in the ceremony but Katsuki felt the need to return the sentiment, explain just how much he had come to love the siren.

“With this binding, I make us one. One in mind, one in body and one in soul. You are my partner, my lover, my mate. From this day on I will thank the fates for bringing me to you on that stormy night but most importantly I thank the fates for allowing you to be a human with me on land and a siren with you in the sea. With this, I claim you as mine.”

With that Izuku finishes his binding with the rope, leaning in and kissing Katsuki on the lips. The two twirl around each other slowly, twining their tails into a double helix, the two men from completely different worlds, coming together as one, to be with one another for the rest of their days.

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The legends say that if you sail past the rocky shores where it’s rumoured the Queen Explosion sunk with all her treasure you can hear two beautiful voices singing a duet of love found in the darkest times and finding places where they belong. The sirens' call will lure you in but you’ll always live to tell the tale of the most beautiful song you’ve heard, as it burrows its way into your heart and living there for the rest of your days. The stories say that if you’re lucky enough to hear the song of the sirens who are so irrevocably in love with each other you will find your perfect match, whatever they may be, making it possible for you to spend the rest of your days with them in a happiness that rivals that of the siren pair, passing on a little bit of their magic to you.

It's been said that there’s a pair of men that work so seamlessly together in the lab it’s as if they’re two halves of a whole. They never run into one another and they know what the other wants before they ask for it. They’re at the forefront of the quickly growing area of science known as chemistry. They’ve discovered so much they’re revered in the science world. They say the insatiable curiosity of one and the burning passion of the other made them a force to be reckoned with.  However, how they’ve travelled so quickly to do work all across the globe remains a mystery even to this day.