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Katsuki wakes up to sunlight trying to stab through the gritty crack of his eyelids and directly into the most tender part of his brain.
He shuts his eyes tight and groans but dear gods is that a mistake.
The sound drags rough and painful up an already abused throat that cracks in dryness and then convulses. Katsuki inhales sharply, stomach tensing on a cough that he swallows on reflex, desperately trying to get some moisture back into his system. The movement does nothing to soothe his throat, his stomach heaves, and the coughing won’t be held back.
He surges up onto an elbow as the coughing really takes hold. His throat feels like it’s on fire, like each hacking cough has to claw its way up his throat in order to force itself out of his body. His vision is going blurry with tears and he won’t be surprised if he sees blood speckle onto the sand beneath him.
His throat aches, his stomach aches, he’s gagging on every other cough, but finally, finally, the hacking begins to peter out. He swallows rapidly, finally able to work some saliva down. His stomach tenses on a final aborted cough but he manages to hold it in through sheer willpower.
Katsuki collapses back onto the sand, breath still ragged and unsteady. He throws a hand over his eyes to stave off the beating sun and it all comes back to him as his breathing slowly evens out.
The storm that had seemed to slam into The Eraser and her crew out of nowhere, lighting carving through the night sky and the rigging going up in flames. The ear shattering crack as the flames reached the powder magazine and the resulting explosion that tore off one entire side of the ship.
The explosion had been what had flung Katsuki into the ocean in the first place, Eijirou and Mina screaming his name. He’d landed in violently churning water, ears ringing, vision blacking in and out, disorientated, and barely able to keep his head above the waves.
Bobbing helplessly in the water he remembers feeling relief that Eijirou and Mina hadn’t been caught in the blast and hoping that they and Captain Aizawa had managed to get the last lifeboat in the water before what was left of The Eraser went down.
It felt like he’d floated in and out of consciousness then, barely managing not to inhale any water, but he could have sworn that at some point arms had wrapped around him. He’d let himself succumb to true unconsciousness after that only because he’d thought Eijirou—or somebody from his crew from another of the lifeboats—had managed to reach him.
He thought he’d been safe.
Lying on some beach, shirtless and with the sun beating down on him, sunburn already starting to lick stinging strips over his exposed skin, Katsuki knew he was far from safe.
He was shipwrecked and marooned.
Katsuki was fucked.
He drags his arm away from his face but doesn’t open his eyes. He presses his palms into his eye sockets hard enough that he’s seeing stars and resists the urge to growl. He knows it’d only hurt his already suffering throat.
The sound of waves lapping against shore, usually a calming sound, were only serving to heighten his anxiety, reminding him where exactly he was marooned.
Kaminari had managed a desperate SOS through comms over to Yagi’s ship when their rigging had first gone up in flames. Yagi’s crew were the only other friendly pirates that they knew were nearby. But rescue depended on staying in the general area where they’d sent the distress call, what with their communication tech being blown to smithereens and also at the bottom of the ocean.
Aizawa’s crew had just finished a major raid on a Royal Armada ship and had sailed into less patrolled waters to avoid the incoming privateers the Armada would waste no time sending in pursuit. The waters they’d retreated to were relatively uninhabited, good for losing pursuers, bad for hopes of rescue when this island was probably one of fucking hundreds dotting this area of unsettled ocean. There was no telling how far Katsuki had drifted either, he could be leagues away from where The Eraser had sunk.
To be perfectly honest, Katsuki was surprised he was even alive. From the brief glimpse of beach he’d garnered when he’d shot up in his coughing fit, he hadn’t seen any driftwood large enough to have floated him to safety. What had he managed to grab onto in order to keep him afloat in a storm angry ocean? There was no way he wouldn’t have sunk under the weight of his own clothes if he hadn’t had something to grab onto.
And although Katsuki was grateful to still be breathing, drowning while he wasn’t awake enough to realize what was happening was honestly starting to sound like a better way to have gone than the slow death by dehydration and heatstroke that he was probably looking forward to here.
A voice in his head that sounds suspiciously like Aizawa does the mental equivalent of a head slap, and yeah okay, Captain was right.
Time for Katsuki to stop feeling sorry for himself and actually assess his situation.
He drops his hands from his face but keeps his eyes scrunched in anticipation of the sun still spearing its way in even through closed eyelids. He’s pleasantly surprised when his vision tints red but the spike of pain he’d expected to go along with it isn’t there. Good, looks like the hypersensitivity was starting to wear off.
Katsuki takes one last breath, as deep as his battered lungs will allow, and opens his eyes.
Huge green eyes stare right down at him.
Katsuki scrambles away in surprise, sand kicking up at his flailing, and then he realizes that the eyes are attached to a face, attached to a body that is—
Fucking floating above the strip of beach where Katsuki had been laying.
“What the hell!” Katsuki barks, hands going to his sides on reflex and gripping onto nothing where the hilt of his scimitars should be.
Green Eyes startles at Katsuki’s exclamation and then he’s scrabbling away too, only when he moves, it’s still in midair.
Green Eyes seems to swim away. He throws his torso back and his legs kick forwards, his arms sweep in large arcs through the air and his legs kick in short jerks, as if he really was propelling through water.
Katsuki has a brief panicked thought that somehow the air around him really has turned to liquid. That at any moment, water is going to start flooding into his mouth instead of oxygen, that after everything he’s going to end up drowning anyway.
The thought makes Katsuki want to laugh a little hysterically.
Gods maybe he really had gone and swallowed salt water past the point of no return. Was he still unconscious? Was this all one vivid dream his dying brain was showing him as he slowly expired from having inhaled what felt like a barrel full of ocean water if the ache in his lungs was anything to go by? Maybe he was awake but just actively hallucinating.
Katsuki roughly wipes over his eyes and when Green Eyes doesn’t magically disappear he pinches his forearm, hard.
Nope, Green Eyes is still there.
Floating.
In the air.
They stay there, caught staring at each other, Katsuki with sand starting to scratch uncomfortably at his ass and Green Eyes with his shock of wild green curls undulating slowly around his head like a halo. Again, like he really was underwater.
And that’s when it hits Katsuki.
Green Eyes, whoever he is, is fucking gorgeous.
Those wide green eyes sit atop round freckled cheeks and full lips. And the freckles don’t stop at just his face, they dot every inch of exposed tan skin like constellations in the night sky.
And oh, can Katsuki see a lot of that skin.
Green Eyes is practically naked, the only covering he has on being some type of dark green material that reminds Katsuki of seaweed. It wraps tightly around sections of Green Eyes’ body. Two wide strips of it wrap around the sides of his chest, following the bottom curves of his pectorals. They flow down the sides of his stomach, framing well defined abs, thinning as they reach towards his bellybutton. More thin strands start out high at his waist and flow down with the curve of his obliques, flowing into hundreds of tendrils of the same material that wrap around the entirety of Green Eyes’ hips. Long strands of those same tendrils hang from the middle of the wrap, falling like a seaweed version of a sarong down the middle of very sturdy looking thighs. The strands seem to sway in the air, much like Green Eyes’ hair.
Katsuki keeps following the line of his legs and has to hold back a gasp as he realizes that Green Eyes’ legs start to fucking disappear mid-thigh. Well, no, disappear isn’t quite the right word. His legs don’t just fade from existence, rather they start to lose detail and color. The tan fades away and flesh becomes more and more translucent until Katsuki can see through it into the blue ocean behind.
It was like Green Eyes’ legs became water that somehow, impossibly, held together in the form of legs and feet. Katsuki wonders, suddenly, what would happen if he laid hands on Green Eyes’ calves. Would his hands just sink into his body like they would sink into a pool of water?
And water drips from every inch of Green Eyes’ normal flesh. He’s sopping wet and dripping, only instead of dripping onto the sand below, the droplets that cascade off his skin catch and float in the air, like they too were caught in the tide pull of his body.
There are shells in his hair, shiny sea pebbles that float around his head like a tiara, dangle from his ears, and wrap like bangles around his wrists and ankles. But much like his hair though they ebb and flow through the air, not attached to Green Eyes with anything tangible.
A bright flash of light brings Katsuki’s attention to Green Eyes’ neck, the sides of which are covered in what looks to be iridescent, pale green scales. They catch in the sun again as the skin there slits and flares outwards. Katsuki has no idea what he’s looking at until he abruptly realizes that Green Eyes has gills on both sides of his neck. Those same pale scales cover the outside of Green Eyes’ biceps and arms. Though his right arm is a mess of scars that run down from his shoulder all the way down to his hand. The scales on that arm are patchy and sparse.
Katsuki looks back at those green eyes, a color which he can now fully comprehend is a verdant so beautiful and bright it’s inhuman.
“I have to be dying,” Katsuki finally utters, out of a loss of anything else to say when the silence continues to stretch.
“Uh, no,” Green Eyes responds, brows furrowing, “you were dying, that’s why I rescued you.”
“You talk, of course you do.”
And then Katsuki throws his head back and laughs, a bit of that hysteria from earlier tinging it because his ship had exploded, he didn’t know if any of his crew had survived, he’d almost drowned, and apparently the only reason he hadn’t was because some magical floating man had saved him.
Those green eyes narrow, brow pinching further.
“Why wouldn’t I be able to talk?” he says and he sounds almost accusing.
“You are a magical floating creature,” Katsuki responds, “I’m still not entirely sure you’re real, excuse me for being a bit surprised that the magical floating creature talks, on top of magically floating and having magical transparent legs. And fucking gills.”
Those eyes narrow further, and the bright of them flashes dangerously. His cheeks get rounder as he bares his—gods—very sharp teeth in a half snarl.
“I’m not a creature,” he says, voice going low and...strangely melodic? “I have a name. It’s Izuku.”
Katsuki can feel the sound in his chest, as if he can parse out the individual vibrations washing against his skin somehow. There’s a low roaring starting in his ears, it’s distracting.
“Hah?” Katsuki says as he shakes his head and paws at an ear.
“I said,” Izuku says, carefully enunciating each word as he fists his hands at his sides, “I’m not. A. Creature.”
Izuku’s voice is layering weirdly. That low threatening growl is the main bass note but there’s a higher, sweeter, overtone that flickers painfully in and out of Katsuki’s hearing range. The roaring in Katsuki’s ears gets louder, sounding like waves crashing against each other, like the ocean in the storm that had taken down his ship.
Only, the sound is entirely in Katsuki’s head, building and echoing until it’s deafening.
Katsuki slaps a hand to his head and staggers as violent waves crashing against his skull. It feels like at any moment they’re going to crack through the bone entirely.
And then abruptly it all stops.
“Shit, I’m sorry!” Izuku exclaims, voice gone from growl into harried alarm. He sounds much closer than he’d been before.
Katsuki looks up and sees Izuku swimming his way. He takes more stumbling steps backwards.
“What the fuck!” Katsuki shouts shakily. “What the hell did you do?”
Izuku freezes looking upset.
“I didn’t mean to—” he says hastily then cuts himself off. He brings his unscarred hand up in a calming gesture. “I’m sorry,” he says evenly, “it’s just...it’s been a long time since I’ve interacted with a human, I forgot to pull my Voice back. It was an accident; it won’t happen again. I promise.”
“What?” Katsuki says as he stares at him uncomprehendingly, “What the hell are you?”
Izuku takes a slow breath and then gently floats downwards. His legs straighten down under him as he does and when translucent feet finally touch sandy beach, they lose their translucency. Freckled skin suddenly becomes solid again and it comes as little surprise that more of those pale scales cover his shins down to the tops of his feet. Izuku’s hair, clothes, and jewelry continue to undulate softly around him though.
He doesn’t move any closer to Katsuki but his face does a complicated dance of emotions. He finally settles on something close to resignation towards the end. He closes his eyes, takes another deep breath, and says, “I’m a siren.”
Katsuki gapes.
A siren?
The mythical creatures that lured sailors to their doom with nothing but the power of their voice? Katsuki had half believed they weren’t real, even if Aizawa swore on The Eraser’s resident cat that they were.
“You’re shitting me,” falls out of Katsuki’s mouth.
Izuku looks affronted.
“I am not shitting you,” he huffs, “why would I lie to you? I was floating in mid-air! I accidently used my Voice on you! Humans can’t do that!”
“Sirens aren’t real,” but even as Katsuki says it he knows he’s wrong. He’s looking at proof that they do. A minute ago, it’d felt like his head was going to explode because Izuku had growled at him.
Izuku just looks at him like he’s stupid.
Which, fair.
But what the hell did a siren want with him?
Katsuki tries to back away some more, only to collide with the rough bark of a palm tree. He reaches for his scimitars, guard firmly up, only to be reminded that they are probably somewhere at the very bottom of the gods damned ocean. He feels naked without any weapons, not counting the fact that he is actually shirtless.
“Well, what the hell do you want with me?” he spits, “Because if you’re here to kill me, I’m not going down without a fucking fight.”
Even if death by siren still sounded marginally better than death by exposure.
Izuku rolls his eyes so hard Katsuki’s surprised they don’t get stuck that way.
“Sirens don’t harm humans,” he says testily, “if anything, humans are the ones who harm sirens. It was a human who gave me all these,” he gestures to the multitude of scars on his arm. “Besides, why would I rescue you just to kill you later?”
“What?” Katsuki says. He’s starting to sound like a damn parrot.
“I rescued you after you were blown off your ship, you passed out soon after you hit the water.” Izuku says irritably, “Why would I save you from drowning and drag you to safety only to kill you after?” Izuku shakes his head dismissively. “Now, I gave you my name, isn’t it only fair that you give me yours?”
Katsuki is still reeling from the implication that there had been someone who’d wrapped his arms around him as he’d lost consciousness—it just hadn’t been Eijirou—that he answers the question without thinking.
“Katsuki,” he responds, “my name is Katsuki.”
Izuku’s features soften, just the tiniest bit.
“Katsuki,” he repeats slowly, like he’s trying to feel the weight of each syllable on his tongue, and his voice goes weird again. There’s that extra layer added, only this time it’s a low rumbling tone underneath Izuku’s regular speaking voice.
And suddenly Katsuki isn’t on some beach, he’s safe and lounging in The Eraser’s crow’s nest, warm wind ruffling his hair as he watches the sun go down over the horizon, painting the water in brilliant shades of red and orange.
Something pulls at his chest, but it doesn’t feel bad this time, it feels...warm.
Katsuki shakes his head, trying to dispel it.
“Hey,” Katsuki complains, “cut that shit out, you said you weren’t going to do...whatever the hell that is anymore!”
Interestingly, a faint blush appears at Izuku’s cheeks.
“Sorry,” he hastily replies, “I swear I’m not doing it on purpose.”
The feeling in Katsuki’s chest dissipates immediately. He feels a strange sense of loss as it goes.
Gods, Izuku really is a fucking siren.
A siren who’d apparently decided to save a drowning pirate despite his very obvious dislike of humans. What was up with that?
“Why did you save me?” Katsuki asks suspiciously, “you don’t seem to like humans too much. And as you said, humans—the ones who believe in you at least—don’t like you that much either.”
At the question, Izuku shuffles, sand sticking to his feet as he does. He wraps a hand around his right wrist bringing it close to his body, almost protective of it. He looks...uncharacteristically hesitant all of a sudden.
“Do—” Izuku starts and stops instead of answering, “Do humans have soulmates?”
“The hell does that have to do with anything?”
“Well, do you?” Izuku asks again undeterred, some of that earlier attitude bleeding back in his tone.
“Yes,” Katsuki responds, still confused, “but they are very few and far between. The chance that you’ll just bump into the one person that’s fated for you is extremely low, so most everyone lives their life without a soulmark ever appearing on their skin.”
“Sirens have soulmates too,” Izuku says, still tentative.
Katsuki arches a brow.
“Okay,” he draws out.
Izuku seems to wrestle with himself for a moment until he finally lets out an exasperated sigh.
“That’s why I saved you.”
“What?”
Izuku rolls his eyes but doesn’t answer, just thrusts his right hand forward with the bottom of his wrist sticking up.
On it, Katsuki sees an inky black tattoo. Ah, a soulmark. Though this one, much like everything else about Izuku, seems magical. The black intertwining lines ripple prettily across Izuku’s skin.
Katsuki frowns.
“Good for you and whatever other fish your soulmate is but I still don’t understand what that has to do with me—”
Izuku lets out an explosive huff of air and then stomps his way over to Katsuki. His hand shoots out to grab Katsuki wrist and then yanks it up, practically shoving it into Katsuki’s line of sight.
It takes a moment for Katsuki to focus on his own hand but when he does—
On his wrist sits an exact copy of Izuku’s soulmark, complete with crisp black lines that seem to move of their own accord.
“Oh,” he says roughly, “shit.”
“Yeah,” Izuku says and he sounds despondent, “just my luck that my soulmate is apparently a human.”