Chapter Text
The sea was too calm.
That was the first thing Shoto noticed as he drifted upward from the deep.Not peaceful, Not gentle, Calm.
Still in a way that felt deliberate, as though the ocean itself were holding its breath.
Above him, the surface shimmered like a sheet of blue glass, fractured by sunlight. Gold spilled through the water in trembling ribbons, catching on the shifting scales of fish and the pale branches of coral far below. The current was soft today, barely tugging at his hair, barely brushing across the delicate fins along his hips and tail.
It made the world feel suspended, Secret.
Like the sea was giving him a moment before it remembered he was not supposed to be here. Shoto Todoroki, youngest prince of the Deep Kingdom, moved through the water with quiet, effortless grace.
His body was long and lithe, made for gliding through endless blue. His skin held the faint pearlescent glow of moonlit shells, pale and smooth beneath the sun filtered water. His hair floated like silk framing his face half white as the moonlight, half red as the coral that grows in the deep eastern Atlantic. Tiny pearls had been braided gently into a few strands, each one shimmering and catching the light whenever he turned his head.
His tail moved behind him in slow, powerful sweeps. It was large and elegant, longer than most merfolk his age, the scales glimmering in shades of pearlescent white and deep crimson red. The colors blended together like spilled blood in the water. His fins were even more striking, long, wide, and ruffled, blooming from his tail in layers that moved like chiffon underwater. At the root they burned crimson, rich and dark, then gradually softened outward into translucent white, so delicate at the edges they looked almost like smoke in water.
He was beautiful in a way that had always made others stare, royal and regal. A creature carved from the most breathtaking parts of the sea.
Shoto tilted his head upward, The surface gleamed above him. His mismatched eyes reflected the light, one clear turquoise blue, bright and calm as shallow tropical water; the other grey like storm dark like waves crashing against jagged cliffs.
A prince was not meant to wander.
A prince was not meant to drift near the surface.
A prince was not meant to look at human ships with longing.
His father’s voice lived inside his skull, deep and cold as the trenches.
The surface is filth.
Humans are greedy.
They will hurt you.
You belong below.
Shoto’s fingers curled slightly in the water, And still, he swam higher. He had been doing this for months, At first, he had only gone as far as the upper reefs, where the water warmed and brightened and schools of fish scattered around him in flashes of silver and yellow. Then he had dared to rise close enough to see the underside of boats. Then close enough to hear human voices muffled through the waves.
And eventually close enough to watch them. He did not know exactly when fascination had become obsession.
Maybe it had begun the first time he saw human children laughing from the shore, their feet splashing in water that barely reached their ankles. Maybe it was the first time he heard music drifting from a passing merchant vessel, strange and bright and messy, nothing like the haunting songs of the deep. Maybe it was the first time he saw bright light flickering on the deck of a ship at night and realized humans carried stars with them wherever they went.
Whatever the reason, Shoto always returned.
Again and again.
Even when he knew he shouldn’t, Even when the guards began watching the palace tunnels more closely. Even when his older siblings warned him that Enji’s temper had been worse lately, that the storms had been stronger, that the king’s mood could blacken the whole sea if provoked.
Shoto still came.
Because up here, just beneath the surface, the water did not feel like a cage.
It felt like possibility, freedom.
His tail flicked once, and he rose the final few feet.
The ship came into view slowly.
A dark shape moving over the water above him, huge and beautiful in its own rough human way. Its hull cut through the calm sea with a steady groan of wood and iron. Sunlight glinted off wet black planks. Heavy ropes hung from the sides, swaying with the vessel’s movement. Above, black sails stretched wide and proud, catching the breeze like wings.
Shoto’s lips parted softly, He had seen this ship before, Not many times, Only twice.
But he remembered it.
It was larger than the merchant ships and faster than the fishing boats. Its crew moved with a sort of wild confidence Shoto found impossible not to watch. They shouted at one another constantly, but there was fellowship beneath it. Familiarity.
They laughed too loudly, Argued too dramatically. Threw ropes and tools and insults around as though none of it could ever truly hurt them.
Pirates, Shoto had once heard one of the older merfolk whisper with disgust.
Dangerous humans.
Greedy Thieves of the surface.
The worst sort of humans.
Shoto had not understood why that made them sound so much more interesting.
He drifted beneath the ship, careful to stay hidden in the glittering distortion under the waterline. Above him, boots thudded across deck boards. Voices carried over the calm sea.
“Oi! Sero, if you drop that rope again, I’m tying you to the mast myself!”
Someone laughed. “You’d miss me too much, Bakugo!”
“I’d sleep better.”
More laughter.
Shoto’s attention sharpened.
Bakugo.
He knew that voice, He had heard it once before during a night when the pirate ship had anchored near a cluster of rocks. He had hidden among kelp and listened to the blond human yell for nearly an hour at a red-haired crewmate who had apparently tied several knots wrong on purpose just to annoy him.
At the time, Shoto had found the human loud.
Abrupt,Almost frightening. But also fascinating.
Today, he saw him properly, The blond human was hanging over the side of the ship.
Thick ropes were looped securely around his waist and thighs, holding him suspended just above the water as he worked along the row of cannons built into the vessel’s side. He had one boot braced against the hull, one hand gripping a rope, while the other tightened something on the cannon mount with quick, practiced movements.
He looked dangerously comfortable there, half-dangling over the open ocean as if falling into it were merely an inconvenience.
The wind tugged at his hair, Sunlight caught in the messy blond spikes, turning them almost gold. He was broad-shouldered and strong, his rolled sleeves revealing forearms corded with muscle. Every movement looked sharp and certain, like his body was always seconds away from a fight.
Shoto hovered beneath him, transfixed. Humans were not supposed to be beautiful, At least, not like this.
Not with sun-warmed skin and hair the color of starlight. Not with sharp garnet eyes that flashed every time someone above annoyed him. Not with a sharp mouth constantly pulled into either a furious scowl or a dangerous smirk.
The blond human wiped sweat from his brow with the back of his wrist, muttering something under his breath. A cool breeze swept across the water just then, lifting the edges of his shirt and stirring his hair. He closed his eyes for a brief second, face tilting slightly into the wind.
Shoto’s chest tightened. There was something in that expression, Something unguarded. A split second where all the sharpness softened, He looked free, Painfully free.
Shoto moved closer before he could stop himself, His tail stirred the water in a slow ripple. Crimson and white fins drifted behind him, almost glowing beneath the surface. He knew he should stay lower, He knew the water was clear. He knew humans had keen eyes when they were looking for treasure, danger, or strange things in the sea.
But the blond human was so close, Close enough that Shoto could see the shape of his mouth.
Close enough to notice a scar near one eyebrow.
Close enough that if he rose just a little more, he might hear his breathing.
Above him, Bakugo shifted his weight, reaching for another tool tied to his belt.
Then he paused.
His brows drew together, Slowly, as if some instinct had hooked into his spine and pulled, he looked down.
Their eyes met through the water,The entire world went quiet.
Katsuki Bakugo had known the sea his whole life. He had seen it in every mood, Glittering and playful beneath a summer sun, Black and vicious under winter storms. Calm enough to reflect the stars, Cruel enough to swallow men whole without leaving a trace.
He respected it. Feared it, though he would bite his own tongue off before admitting that aloud, But he had never looked into the sea and felt it look back.
For one impossible moment, Katsuki forgot where he was. Forgot the ropes biting into his hips, Forgot the cannon beneath his hand. Forgot the ship, the crew, the heat of the day, the salt drying on his skin, Because beneath the water, staring up at him with wide mismatched eyes, was a face so beautiful it stole the breath straight out of his lungs.
At first, Katsuki thought it was a trick of light.
Some reflection, Some sun-drunk illusion born from too many hours at sea.
But then the creature blinked, Slowly, Curiously.
Katsuki’s fingers tightened around the rope.
“What the…”
The face beneath the surface tilted, Not frightened, Not exactly. Cautious, maybe, But curious too. The creature’s hair floated around his face like silk in the current red and white, soft-looking even underwater, threaded with pearls that glimmered like tiny moons. His eyes were the worst part, The prettiest part. One was blue, so clear and bright Katsuki thought of tropical shallows where the sand shone white beneath the water. The other was grey, darker, heavy like the depth of the north sea.
No human had eyes like that, No human had fins drifting behind them in crimson- white waves. No human looked like he had been born from the secret places of the ocean.
Katsuki’s heart slammed hard against his ribs. He should call out, He should shout for All Might, He should tell the crew there was something in the water. Instead, he leaned closer. Then the creature was moving upward, slowly and gracefully.
As if drawn by the same invisible thread pulling Katsuki down, Water broke around him with barely a sound. First the crown of his head, then his eyes, then his mouth and shoulders rising into open air. Wet hair clung to the pale skin of his jaw and neck, Pearls gleamed among red and white strands. Droplets slid down his cheeks and throat, catching in the hollow at the base of his neck before rolling lower.
Katsuki’s mouth went dry.
The creature rested one hand against the side of the ship, fingers pale and delicate but tipped with faintly shimmering nails. His shoulders were bare, his skin luminous under the sun, and beneath the water Katsuki could see vague flashes of a large tail shifting lazily to keep him afloat.
A merman.
The thought struck him so violently he nearly lost his grip.
A damn merman.
Every sailor had stories, Every tavern near every port had some drunk bastard claiming he’d seen one. Beautiful faces, Sharp teeth, Voices that could lure men to death. Monsters wearing pretty skin.
Katsuki had never believed any of it, He believed in what he could touch, What he could fight, What he could feel.
But this… The merman looked up at him with open wonder, Katsuki felt something inside him tilt. Not fear exactly, Something worse.
A fascination so immediate and intense it felt like stepping too close to a flame.
“Who…” Katsuki started, but his voice came out rougher than he wanted. He cleared his throat, hating the way his pulse was thundering like he had just sprinted across the deck. “Who are you?”
The merman blinked at him, He did not answer. Maybe he couldn’t understand, Maybe he chose not to. Instead, he rose a little higher, the water slipping down his chest as his tail gave one slow, powerful flick beneath the surface.
Katsuki stared at the movement without meaning to, He caught a glimpse of scales, Pearl-white and crimson.
A tail so long and strong it looked like it belonged to something ethereal, iridescent and shimmering every time it catches the sunlight. The fins were enormous, ruffled and flowing, crimson bleeding into translucent white like silk dipped in blood and foam.
Beautiful.
Enchanting.
Captivating.
Katsuki’s thoughts tripped over each other, The merman lifted his hand carefully and slowly, As if Katsuki might bolt.
Katsuki almost laughed at the absurdity of that. Him? Bolt? From anything? But then those pale fingers reached toward him, and Katsuki realized he was the one holding perfectly still.
The distance between them narrowed to inches.
Katsuki reached too, He did not know why. Could not have explained it if someone pressed a pistol to his head, He only knew he had to know if the creature was real, Had to touch him once. Had to prove he was not losing his mind.
Their fingers were just about to meet when the ship jerked violently beneath him, Katsuki’s shoulder slammed into the hull.
The merman flinched back, Above them, a bell rang.
Once.
Twice.
Then chaos tore across the deck.
“STORM!”
The shout cracked through the air, Katsuki snapped his head upward, the sky had changed. It had been blue only moments ago, bright and cloudless except for a few white streaks near the horizon. Now, an enormous bank of black clouds rolled toward them with unnatural speed, swallowing the sun piece by piece. The wind shifted violently, no longer cool and playful but sharp, cold, carrying the metallic scent of rain and lightning.
“Secure the sails!” Captain Toshinori roared from above. “Batten down the hatches!” His voice was massive enough to cut through panic, steady and commanding even as the ship lurched again. “All hands on deck!”
Crew members scrambled across the deck.
Katsuki looked back down, the merman had gone rigid. His face had changed entirely, the curiosity was gone, replaced by something sharp and fearful. Not fear of the storm itself, Katsuki realized vaguely, but recognition.
Like he knew what caused this storm.
From somewhere above, Sero’s voice shouted over the rising wind. “KING ENJI MUST BE IN A SHIT FUCK MOOD!”
A few crew members cursed.
Katsuki every pirate and sailor knew who King Enji was, a myth said to be the king of the seas, often used as the reason for bad weather and storms, but the merman’s eyes widened at the name.
That was enough to make something cold scrape down Katsuki’s spine, he tightened his grip on the rope and met the creature’s gaze one last time. For a heartbeat, neither moved, rain began to fall between them.
The merman looked like he wanted to say something, Katsuki did too, though he had no damn idea what. Then another wave slammed against the ship, and duty tore him away.
“Bakugo!” Kirishima yelled from the deck. “Get up here!”
Katsuki cursed under his breath and hauled himself upward, muscles burning as he climbed the ropes back toward the rail. When he glanced down again, the merman was still there, half-hidden in the darkening water, watching him with those impossible eyes, Then the rain swallowed him from view.
The storm hit like a living thing, there was no gentle buildup. No warning beyond the sudden blackening sky. One moment the ship was cutting steadily across calm water, and the next the ocean rose around them in furious walls.
Waves crashed over the deck hard enough to knock men off their feet, rain lashed sideways, blinding and cold. The sails snapped violently overhead, ropes whipping through the air as thunder boomed so loudly the whole ship seemed to shudder beneath it.
Katsuki moved on instinct, he was naturally talented at whatever he tried to do and quick witted, but at sea none of that mattered unless he could move faster than disaster. He grabbed ropes, barked orders, shoved a panicking deckhand toward safety, then sprinted toward the cannons as the ship pitched hard to one side.
“Lock them down!” The Captain shouted.
“I’m doing it!” Katsuki snapped, though the captain probably couldn’t hear him over the storm.
The cannons were dangerous in weather like this, Too heavy and loose if the ropes failed. If one broke free, it could crush a man or punch straight through weakened wood.
Katsuki dropped beside the nearest cannon, soaked to the bone within seconds, his blond hair plastered to his forehead. Saltwater stung his eyes, his fingers moved fast over wet rope, tightening knots, checking braces.
The ship tilted.
A cannon groaned.
“Shit.”
Katsuki threw his weight against it, boots skidding on the slick deck. Another wave slammed over the side, chest-high and brutal. He choked on seawater but held on.
Somewhere to his left, Sero yelled.
Kirishima shouted back.
Wood cracked overhead, the world became rain and thunder and screaming wind.
Then Katsuki felt it, A violent snap beneath his hand. The rope securing the cannon tore loose.
The ship dropped suddenly beneath him, falling down the side of a wave. For one breathless second, Katsuki was weightless, Then the cannon lurched.
It slammed into him hard enough to knock the air from his lungs, his boots left the deck. He heard Kirishima scream his name, and then there was only water.
Cold.
Dark.
Violent.
The ocean swallowed Katsuki whole, he hit hard enough that pain flashed white behind his eyes. The storm torn sea dragged him under instantly, twisting him, spinning him, shoving saltwater into his mouth and nose.
He kicked hard, but his boots were heavy, his clothes dragged him down. He reached for the surface, but there was no surface only black water and foam and the roaring pressure of the sea crushing around him.
For the first time in years, real fear punched through Katsuki’s chest. Not panic, He refused to panic. But fear, Sharp and animalistic.
His lungs burned, as his hands clawed at the water. Something struck his shoulder, debris maybe. He couldn’t tell, his vision blurred. The world above him flashed briefly silver with lightning, then disappeared again as another current rolled him deeper.
He was going to drown, the thought came with terrifying clarity. Not in battle, not with a blade in his hand. Not standing on deck with the rest the crew around him.
But here.
Dragged down in the dark by a storm that had come from nowhere.
His chest convulsed, bubbles escaped his mouth, then arms wrapped around him, Strong arms. Katsuki’s fading vision caught a flash of pale skin, red-and-white hair, fins flaring wide against the dark water.
The merman.
Katsuki’s body was too heavy to respond, he felt himself pulled firmly against a cool chest, one arm locked around his ribs. A powerful tail snapped through the water, cutting against the current with astonishing force. The storm fought them, Waves churned above. Debris tumbled past, but the merman did not let go.
Katsuki’s consciousness flickered.
For a moment he thought he heard singing, not words, just sound. A soft hum vibrating through the water and into his bones, then everything went black.
When Katsuki woke, he thought he was dead, It was not an unreasonable conclusion. His body hurt everywhere, his lungs felt scraped raw, his throat burned with salt. He was floating on something unstable, the world beneath him rocking gently instead of pitching violently. Rain still fell, but softer now, tapping against wood and water.
He opened his eyes slowly, the sky above him was grey, not black anymore. The storm had begun moving away, Clouds churned in the distance, lightning flickering faintly inside them, but overhead the rain thinned and patches of pale light broke through.
Then something brushed his cheek, Katsuki turned his head and forgot how to breathe all over again. The merman was beside him, He had dragged Katsuki onto a cluster of broken wooden planks lashed together by tangled rope and wreckage. One arm was still around him, holding him carefully against the debris so he would not slip back under. Wet red-and-white hair clung to the merman’s face and neck. Pearls gleamed faintly among the strands.
He looked worried, actually worried. His mismatched eyes searched Katsuki’s face with a softness that made Katsuki’s chest ache in a way he did not understand.
The merman reached up and brushed wet blond hair away from Katsuki’s forehead.
His touch was gentle, absurdly gentle.
Katsuki stared at him.
“You…”
His voice came out wrecked.
The merman’s face brightened instantly, relief softened his mouth into the smallest smile Katsuki had ever seen.
Then, before Katsuki could move or speak or regain any sense at all, the merman leaned in and nuzzled his cheek.
Katsuki froze completely, It was not a kiss. It was more innocent than that, more instinctive. A brush of cool skin against his, soft and affectionate, as though the merman was simply glad he was alive and did not know any other way to show it.
Katsuki’s entire body went hot, his heart gave one violent, traitorous kick. He had been touched before, Punched, grabbed, shoved, clapped on the back by crewmates, kissed sloppily in taverns by people whose names he never bothered remembering.
But nothing had ever felt like that. Like being handled carefully, like being something worth saving.
The merman pulled back just enough to look at him, then he hummed softly. The sound slid through the air between them, low and haunting and impossibly beautiful. Katsuki felt it settle under his ribs. The melody was simple, almost wordless, but there was something ancient in it. Something deep-sea and moonlit, It sounded like lonely currents moving through coral caves, Like whales singing miles beneath the surface. Like a secret the ocean had carried for centuries and was finally whispering into his ear.
Katsuki should have been afraid, Sailors told stories about merfolk songs. How they lured men from ships, how they wrapped around a person’s mind and pulled them into the sea smiling. But this did not feel like a trap, It felt like comfort and that scared Katsuki more.
He stared at the merman’s mouth as he hummed, at the soft curve of his lips, at the droplets clinging to his lashes. He thought wildly, stupidly, that no creature had any right to be that beautiful after nearly drowning him in wonder twice in one day.
No, not drowning him, Saving him.
The realization hit hard.
“You saved me,” Katsuki rasped.
The merman tilted his head.
Katsuki lifted one shaking hand, he did not know what he meant to do until his palm touched the merman’s cheek, the merman went very still. His skin was cool from the water but not cold, smooth and real. Beneath Katsuki’s thumb, he felt the faintest movement as the merman leaned into him.
Trusting.
Katsuki’s throat tightened.
“You’re real,” he whispered, almost angrily, because it felt unfair. Impossible things should stay impossible, Beautiful things should not appear out of the sea, save his life, hum to him like he mattered, and then look at him like that.
The merman smiled again, this time wider. A small, secret smile, Katsuki’s stomach dropped.
Oh.
Oh, he was in trouble.
Not the kind of trouble he could punch his way out of. Not the kind he could curse at until it backed down. This was worse, This was red-and-white hair and mismatched eyes and a hand resting lightly over his wrist, fingers delicate but strong. This was the sound of a song he already knew he would dream about. This was the sea giving him something precious and terrifying, and Katsuki having no damn idea what to do with it.
Then distant voices shattered the moment.
“BAKUGO!”
Katsuki jerked.
The merman’s head snapped toward the sound.
Through the thinning rain, a small rescue boat cut across the water. Behind it, the pirate ship loomed battered but intact, sails torn and deck crawling with frantic movement.
“KATSUKI!”
Kirishima. Alive, Close.
Relief should have been the only thing Katsuki felt, Instead, panic clawed through him.
The merman’s expression shuttered, He looked toward the approaching boat, then back at Katsuki. His hand slipped away.
“No,” Katsuki said before he could stop himself.
The merman paused.
Katsuki did not know what he was asking, Don’t leave? Stay? Tell me your name? Let me see you again?
All of it tangled uselessly behind his teeth.The boat drew closer. Sero’s voice carried across the water. “I see him! He’s on debris!”
The merman began to sink backward into the sea. Katsuki grabbed his wrist, not hard. But desperately enough that the merman’s eyes widened.
For a moment they stared at each other, rain slid down Katsuki’s face, his hand trembled around the merman’s wrist, whether from cold or exhaustion or something far more humiliating, he didn’t know.
“Who are you?” Katsuki asked again, softer this time.
The merman’s lips parted. For one perfect second, Katsuki thought he might answer.
Then Kirishima shouted again, closer now, and fear flashed across the merman’s face.
Not of Katsuki, Of being seen. Katsuki felt it immediately and hated it, slowly, he let go.
The merman looked down at his released wrist, then back up at Katsuki, There was regret in his eyes. Regret so human it hurt.
Katsuki reached out one last time and cupped his cheek, The merman turned into the touch as if he could not help himself. Katsuki’s thumb brushed once over smooth skin.
“I’ll find you,” he whispered, reckless and stupid and barely audible over the waves.
He did not know if the merman understood, But the merman’s eyes softened. Then he slipped beneath the surface, One moment he was there, The next there was only a flash of crimson-white tail beneath the water, fins blooming wide before vanishing into blue.
Katsuki stared after him.
Empty.
Cold.
Suddenly furious at the entire ocean for taking him back.
Then strong arms hauled him roughly into the rescue boat. “Katsuki!” Kirishima nearly crushed him in a hug before seeming to remember he had almost drowned. “Shit, man, you scared the hell out of us!”
“Get off,” Katsuki muttered weakly, though he barely shoved him.
Sero laughed shakily from the other side of the boat, face pale with relief. “You look like a drowned rat.”
“Say that again and I’ll throw you in.”
“You nearly died and you’re still threatening me. Good to know you’re fine.”
Kirishima grinned, but his eyes were wet.
The crew cheered when they got him back to the ship.
Hands clapped his shoulders.
All Might himself gripped the back of Katsuki’s neck with huge relieved strength and said something about being reckless and stubborn.
Katsuki heard none of it clearly, He stood dripping on deck, wrapped in a rough blanket someone had shoved around him, and stared over the railing at the sea.
Searching, waiting.
His heart still beat too fast, His skin still tingling from the merman’s touch. His ears still held that song.
“Katsuki?” Kirishima asked quietly beside him. “You okay?”
Katsuki’s jaw tightened.
He looked out across the glittering water, now calm again as if nothing had happened. As if the storm had never existed, As if the sea had not opened up and shown him something that had already carved itself into his bones.
“I saw something,” he said.
Sero leaned in from behind. “Like your life flashing before your eyes?”
Katsuki did not answer.
Because how the hell was he supposed to explain it?
A merman beneath the waves.
A beautiful creature with pearls in his hair.
A song that made Katsuki feel like he had been drowning long before he ever fell into the sea.
Far below, hidden beneath layers of blue, Shoto watched the pirate ship from a distance. He kept one hand pressed over his own cheek, Where the human had touched him.
His heart beat strangely, too fast, his chest was too warm.
He watched as the blond human stood at the railing, still looking for him. A soft ache bloomed beneath Shoto’s ribs.
Then the water around him shifted, The temperature rose . A current rolled through the deep, heavy and furious.
Shoto’s blood went cold, His father.
The storm had not been random, Of course it had not been random. King Enji’s anger had shaken the sea again, and Shoto had been close enough to the surface to feel the warning too late.
He turned away from the ship reluctantly.
Away from the human with sunlight hair and burning red eyes. Away from the first person above the water who had looked at him and not tried to harm him.
Shoto dove.
His powerful tail cut through the water, crimson and white flashing once before disappearing into the deep.
Behind him, the surface grew distant, The sunlight faded. The sea darkened around him, and still, as he rushed home toward his father’s wrath, Shoto found himself humming softly. The same tune he had sung to the human. The same tune Katsuki Bakugo would hear in his dreams long after the ocean had gone quiet.