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canned tuna and gas station sushi

Summary:

Barely coping with a devastating loss, Hakuji is meandering through life. Despite taking over Keizo's dojo, he knows he's not living the way Koyuki and Keizo would have wanted for him.

Then a half-dead siren washes up on the beach, and for the first time in years, Hakuji has someone he needs to stay alive for, someone he needs to take care of.

And despite waking up in a bizarre new place, barely alive after a brutal fight, Kyojuro can't help but be intrigued by the human that dragged him home with him.

Notes:

This was.... supposed to be a one-shot.... But as we can all tell by now, apparently I can't do shit in moderation. I got 5K words into this and NOTHING was developing quickly so I just bit the bullet and it's multi-chap now

This is also my first time writing a complete AU not connected to canonverse in a HOT minute, and my first time EVER doing it for demon slayer, so here's hoping it turns out okay....

Anyways, I hope you all enjoy!

(See the end of the work for more notes.)

Chapter 1: a discovery

Chapter Text

Early rays of the rising sun over the ocean were always a pleasant sight. Especially on these cool winter mornings. They did little to genuinely stave off the chill, but Hakuji could imagine himself a little warmer as soon as the sun crested the horizon and the light reflected off the water. It wasn’t quite cold enough for him to see his breath billowing through the air, not yet, but his fingers and nose were definitely cold. He probably only had a month or two at most before winter began in earnest and it would be too cold to run out on the beach like this. 

Which sucked. He always had a harder time convincing himself to run if it was on a treadmill in a gym rather than outside. 

He would get over it though. 

Gentle waves washed against the sand, the quiet twittering of birdsong could be heard on the breeze. He focused on the soft crunch of his shoes in the sand. 

The cawing of crows ahead nearly had him faltering, however. He was used the sounds of the seabirds, and softer calls of the birds inland. Crows weren’t all that common on the beach, though. He squinted at the dark specks circling something much further down the beach. 

Mildly curious, Hakuji picked up the pace. He tried to take these jogs slowly, but the closer he got to whatever the thing was, the more curious he became. It was a mound of… something. Something shimmering and golden. Had something washed up on that beach? Why would crows be interested in it? 

“Oh shit.” Hakuji got close enough to make out a tail. A giant, scaled fish tail. Had something died and washed up on shore…? Obviously that had to be the case, but something so huge had to be a rarity. What kind of fish even were that big? 

One of the crows swooped down to peck at the dead thing, and Hakuji grimaced. Should he really get any closer? He was surprised it didn’t reek of dead fish even at this distance given how large the thing was. 

He had to admit… he was very curious about what kind of animal it was. Something so large had to be something at least mildly interesting, didn’t it? And depending on what it was, should he call someone? Some kind of… animal control? Giant dead things on the beach probably weren’t something that should just be left alone, right? 

And then he got close enough to discern the wild mane of hair. Even soaked as it was, the golden color of it shined brilliantly in the early morning sun, and red locks and ends made it all the more beautiful.

“Oh shit.” Hakuji stumbled to an abrupt halt several feet away from the creature, his awe getting the better of him. 

It was one of the merfolk.  

It—They? Hakuji could admit, he didn’t know much about merfolk, but he had heard there was a lot of research to suggest they were just as intelligent as humans, wasn’t there? Regardless, they were curled up in a way that he couldn’t see much of them other than their massive tail and mass of hair. 

A small wave crashed over the beach, and the crow picking at them fluttered back into the sky with a disgruntled caw. The water receded, and thick streams of crimson washed away with it. 

Disappointment welled up within Hakuji. If they were bleeding so profusely, this couldn’t have been a calm or peaceful death. Even this angle of their limp body was enough to tell him this had been a gorgeous creature, and given the sheer size of them, they must have lived a decent life. 

All to wash up dead on a beach. 

Hakuji crept forward a few more steps, rounded the merfolk’s body. How many people got the chance to see one of them up close like this? Not many, that was for damn sure. 

Another wave crashed over them. More blood washed away. 

The scales of their tail and fins matched their gorgeous hair, and Hakuji couldn’t help but try to imagine how beautiful they might have been alive. But that couldn’t distract from the gaping tears in their tail. Given the way they were still oozing blood, the wounds were relatively fresh. One of their fins had been ripped and torn. The vicious claw and teeth marks worked up the merfolk’s entire body. Another gentle wave pushed some of their hair aside, revealing their face, and Hakuji winced at the throat wounds that were revealed. 

Those had certainly been the cause of death. 

Something had torn clean through the creature’s throat, and over the ridged gills on the left side of their neck. He wondered if they’d bled out or drowned first. 

He wondered what the more peaceful death might have been. 

Although… given the state of them, there was no way this death could have been anything but vicious and brutal. 

The ocean careened over them again. Then receded. 

The mer sputtered out a pathetic cough. 

“Holy fuck.” 

They were alive. This mer was fucking alive.

Hakuji crept forward and kneeled down, reaching out without thinking about it. He needed to put pressure on the wounds, and then… call someone? Yeah, yeah, there had to be some kind of crisis line that existed for these types of things, didn’t there? 

He halted just before he hand pressed against the throat wounds. Merfolk could be dangerous. The average person was warned against closely interacting with them, and this one had been horrifically injured. There was a good chance this thing could maul Hakuji if they really wanted to, with a terrifying amount of ease. 

Another pathetic cough forced its way out of the mer’s throat. 

Oh fuck it. Hakuji had to do something, and if he got mauled, he got mauled. What did he really have to live for anyways? And given that the mer hadn’t reacted at all to crows pecking at them, they were probably not aware enough to react to anything at the moment. 

Hakuji pressed his hand against their mangled throat, and did his best to hold the wounds closed. 

The mer didn’t react to his touch at all. Which on the one hand, was a good thing. Hakuji wasn’t getting mauled. On the other, it wasn’t good that they had such little awareness. 

With his free hand, he fished his phone out of his pocket, attempted to open the internet, before groaning at the loading bar that refused to move much at all. 

The signal out here had always been awful. He barely got passable signal in his house, let alone out on the beach. 

But if he just left this mer here, they’d likely be dead by the time he got ahold of anyone. Or they could get washed back out to sea, which was also a death sentence. 

Okay. Okay. He just… had to figure something out. 

He tucked his phone back into his pocket, and quickly slipped out of shirt to rip it into strips. At the least, he needed to slow the bleeding in their throat. The tail wounds were concerning, but nowhere near the level of their throat. For them to still be alive, by some miracle, the major arteries hadn’t been hit, but any throat injuries were dangerous. And he dreaded to think how their gills might have been damaged. 

He tied a strip of his t-shirt around the creature’s throat, as tight as possible without cutting off airflow. It was soaked red within seconds, but it was the best he could do out on the beach with no other supplies. Using the rest of the hastily torn fabric, he tied up as many of the tail wounds as he could. 

The mer’s body was freezing, and Hakuji figured that wasn’t a good sign either, but their blood was warm. Were merfolk cold blooded, or warm blooded? Fuck, he wished he knew anything but the most basic knowledge about them. 

But now that he’d done what he could to tie off the wounds, he… didn’t really didn’t know where to go from here. 

Standing up, he wiped the blood from his hands onto his pants. Or at least tried, but there was so much of it he achieved little more than smearing it further. 

Even doing what he could to halt the bleeding, he didn’t trust leaving the mer out here alone while he went somewhere with signal to try and find someone to call. Especially when he didn’t even know who the fuck to call. Animal control? That couldn’t be right… Merfolk weren’t animals, not exactly. He knew there were all kinds of debates on that particular subject. 

But that didn’t change that he couldn’t do anything else until he did have phone signal, whether that be finding someone to call, or just looking up any information about merfolk in general. 

Or he could just walk away. What did this have to do with him anyways? He wasn’t responsible for this. What the fuck was he supposed to do with a giant half-dead fish? 

A grating, painful breath shuddered out of the mer. 

Hakuji squeezed his eyes shut. 

He hadn’t lasted a year in med school. He didn’t know shit about mers. Chances were he would only make things worse for this one. 

But no one really visited this section of the beach, and certainly not during winter months. If he didn’t do something, they would die. 

Plain and simple. 

He didn’t think as he leaned down to wrap his arms around the mer’s waist and attempted to heave them up. 

Confronted with pure dead weight that Hakuji had not been expecting, he nearly toppled on top of the mer’s body, and yelped, “Oh fuck!” 

The mer still didn’t so much as stir. 

Hakuji could dead lift two hundred and fifty pounds on a good day. 

This felt like more than that. 

It didn’t help that the mer was slippery, both with water and blood. 

And long. So fucking long. Given the way they were curled around themself, Hakuji couldn’t make an overly accurate guess of how many feet long their tail was, but yeah. He was big. Likely too big for Hakuji to easily pick up and carry, not unless he put them on his back and let their tail drag behind. 

Not ideal, but what other options did he have? 

And if he threw his back out… Well… He’d just have to cancel classes for a couple weeks. He could worry about his finances later. 

Better prepared for how heavy the mer truly was, Hakuji grabbed them once again, and heaved them out of the water. Uncoiling their body, he got a better look at them. 

Fully sprawled out, the mer was enormous. Even their torso, despite being mostly humanoid, felt too big. 

Were mers supposed to be this large? Hakuji always thought they were close to humans in size. At least proportionally, right? 

From their head to the end of their tail, the mer had to be at least ten feet long! 

Well, weirdly giant fish person or not, Hakuji wasn’t going to back out now. Ignoring the wet sand and blood caking onto his hands, he rolled the mer onto their stomach, and awkwardly, very awkwardly, kneeled down to work them onto his back, and drape their arms over his shoulders. 

It was only once the mer was draped over his back did Hakuji realize they didn’t have thighs for him to support, as he would have if he carried a human on his back. Fuck. And even with just their torso laying against his back, Hakuji felt like he was damn near being flattened. 

How much did this fucking thing weigh? 

With little options, he gripped the mer’s arms, grit his teeth, and forced himself up on trembling legs. 

Oh yeah. He was definitely going to feel this tomorrow morning. 

He took a step forward, and felt the massive thing’s tail drag behind him. Their head fell limply on Hakuji’s shoulder, and their hair pressed against his face, leaving him sputtering it out of his mouth and desperately blinking it out of his eye. 

Did he seriously think he was going to manage to carry this thing the half-mile back to his house? 

And if he got them to his house, what the fuck was he supposed to do with them? 

For all he knew, interacting with mers like this could be some kind of federal crime, and that really wasn’t something he needed to be dealing with right now. 

He took another step forward. 

Koyuki and Keizo had always said he was too stubborn for his own good. 

He ignored the burning muscles in his thighs and back as he walked. He ignored the too-warm blood dripping down his chest from the wounds in the mer’s throat. 

He ignored how fucking stupid this was. 

He took another step forward. 


Hakuji thanked god he didn’t bother to lock the door when he went on his mornings runs, because fumbling with his keys with a giant mer on his back was the last thing he wanted to fuck with. He let go of one of the mer’s arms, and angled his body in a desperate attempt to keep them from sliding down his back, because Hakuji wasn’t sure if he had the strength to pick them up again today, and fumbled with the door knob. As soon as the door unlatched, he gripped the mer’s arm once again to keep them from sliding further down his back, and kicked the door the rest of the way open. 

He tried not to think about the sand and blood and last droplets of sea water smearing through the living room as he went. He could worry about cleaning later. 

“Where the fuck am I supposed to put you…?” Hakuji muttered as he stood in the center of the living room. 

Mers could breathe air as well as water. Hakuji knew that. But they probably needed to be in water, didn’t they? Whales and dolphins breathed air, but that didn’t mean they were supposed to be completely dry or on land. 

The only place in the house with decent water access was the bathtub. 

This mer was definitely not going to fit in his bathtub. 

But it was only temporary, until Hakuji could figure out who the fuck to call so some actual professionals could come take care of this. 

He stumbled his way to the bathroom, and groaned in relief as he let the mer slide from his back and into the bathtub. 

Then winced at the harsh thud of their landing. 

They still didn’t stir, despite the roughness that Hakuji handled them with. 

He shook his head, and decided not to dwell on it. Worrying that it might be too late to save them would do nothing to help, and as much as he wanted to flop down in the floor and stretch out his aching back, he was far from finished yet. 

He maneuvered the mer’s massive, sinewy tail, doing his best to fit as much of them as possible in the bathtub without the position looking ridiculously uncomfortable. Ultimately, this ended with the mer’s torso propped against the far corner, and their tail flopped over itself in the tub, though that still left a large portion of it dangling over the edge of the tub. 

Hakuji sighed. This was really the best he could do. 

He switched on the faucet, making sure the water hovered somewhere between hot and cold, still unsure of how mers regulated body temperature, before hurrying off to find his actual first aid supplies. 

He hoped they were still under the kitchen sink… He hadn’t touched them since he dropped out, and he hoped he hadn’t thrown them out at some point without thinking about it. 

Thankfully, it was still there, and he rushed back to the bathroom. 

The water pooling in the bathtub was already tinting red. 

Shit. 

As delicately as possible, he unwrapped the blood-soaked t-shirt strips from the mer’s neck, and winced at the damage. The wounds definitely needed stitches, but they sliced through their gills. Would stitching over them worsen the injuries? 

But if Hakuji didn’t stitch them up, there was still a good chance the mer would bleed out. 

He didn’t have a choice, did he? 

He pulled on a pair of gloves, sat on the edge of the bathtub, and began the arduous process of cleaning the wounds. He dabbed at them with disinfectant soaked cotton, and tossed them into the little garbage bin beneath the sink once they got too blood-soaked to be effective. He just wanted to make sure there was no more sand in the wound before sewing it up… But every time he thought he found the last few grains of it, he found more. 

In the silence of the bathroom, Hakuji could more clearly hear the mer’s ragged breaths. They were far from pleasant, but at least they were steady, and relatively deep. Maybe this wasn’t as hopeless as he’d thought at first. 

Leaned so close to the mer, Hakuji allowed his attention to wander. A thick curtain of still damp hair obscured most of their face, but curiosity, for what felt like the millionth time that morning, got the better of him, and Hakuji brushed it aside. 

“Oh.” 

The mer’s face was just as pretty as the rest of them. The same shimmering scales of their tail framed their face, trailed along their jaw. Their ears… were they even ears? Or were they fins? Frills? Whatever the hell they were the same deep red as the tips of their hair. Despite that… their face was rather human in its features. Human, and masculine. 

Did that mean they were male? They had a flat chest… So, probably male, right? 

Shaking his head, Hakuji turned his focus back to cleaning the wounds. The mer’s sex really wasn’t important right now, and he couldn’t get distracted. He needed to clean, stitch, and bandage these wounds as quickly as possible, so he could get this mer out of here and to actual help as quickly as possible. 

Reasonably satisfied that he got all the sand out of the wounds, he reached for the needle and thread. 

Once more, he hesitated as he looked at the gills. What if stitching over them caused permanent damage? What if the mer was never able to breathe out of them on that side again? If so, he might not ever be able to truly survive in the ocean again. 

Hakuji glanced down at the water, and it was already fully clouded with blood. 

Hakuji shook his head, took a deep breath, and pierced the needle through skin and scales. 

He was glad the needle slid through the scales with the same ease as flesh. 

His hands were steady as he stitched up the wounds. He thought he might have been out of practice, considering he hadn’t done this in nearly three years, but it was like second nature. Sink the needle in, pull the thread through, twist. Sink the needle in, pull the thread through, twist. 

It didn’t take long to sew up the first tear, and Hakuji snipped the thread away. 

As he started on the second, he wondered what caused these injuries. Another mer…? Did they really get so violent with each other? 

Then again, humans did kill each other pretty brutally all the time, so maybe it wasn’t all that unusual. Was it bad to hold merfolk to a higher standard? Was it weird? Probably. 

The mer was deathly still as Hakuji stitched up his throat, sewed up his gills. Once again, this was most definitely a blessing, but still concerning. 

Once he was satisfied with the throat wounds, Hakuji turned his attention to the mer’s tail. 

Given the sheer number and size of the injuries, he hoped he didn’t run out of supplies before he stitched up at least the worst of them. 

It was also going to take fucking forever. 

Oh well. He didn’t have any classes to teach on the weekends. What else was he going to do today? Alternate between working out and laying in bed? 

Hakuji reached for the disinfectant, and braced himself for a long morning. 


It was exactly 11:47 by the time Hakuji had stitched the last wound, peeled off his gloves, and tossed them into the little trash bin. 

After that, he reached around the mer’s limp body to drain the bloody water and replace it with clean and fresh water. 

Now that all the blood was gone, the mer looked slightly less like he was on death’s door. 

Hakuji… also began to fully process that there was an unconscious mer flopped into his goddamn bathtub. 

Fuck, he needed a damn cigarette. 

Surely Koyuki would have forgiven him in this situation. 

But before he could relax, he still had to do the research to figure out who to contact about that mer. 

With a tired sigh, he stumbled out of the bathroom and towards the kitchen, every muscle in his body already aching. 

The creaking of the old floors was the only sound in the silent house, which was nothing unusual. However, it was strange to consider that there was someone else here other than Hakuji, even if it was a half-dead mer unconscious in his bathtub. 

No one had set foot in this house other than himself since Koyuki and Keizo had died. 

Although… the mer didn’t have feet, so that was still technically true. 

He pulled his phone out of his pocket as he went. What should he even search for this? Mer crisis line? What to do with injured mer? Who the fuck should I call when I find a half-dead fish person on the beach and bring them to my house because I’m dumb? 

He settled for injured mer. 

That mostly just brought up disturbing images and stories of merfolk being grievously harmed in one way or another. Half dead from animal attacks, mer infighting, and of course, stupid bullshit humans caused. 

Next he tried mer rehabilitation. Maybe there was some kind of rehabilitation center for merfolk somewhere nearby that he could contact? There were all kinds of wildlife centers for that type of thing. 

But of course, there were none anywhere even close to the area. And even the places he found that specialized in mer research didn’t have any on sight. Merfolk were elusive, and difficult to track. There weren’t really any of them living in captivity. 

Hakuji should have expected that there wasn’t even a small research facility anywhere near here. They were out in the damn sticks, and mer sightings weren’t common in the area. What point would there be in research facilities being out here? 

Although… 

Hakuji frowned as he scrolled through one of the facility's websites. There weren’t a lot of photos, but the merfolk in them… did not look exactly like the one in his bathtub. 

Confused, Hakuji just searched up merfolk in general. 

Scrolling through the images, at first glance, they did look a lot like the one currently in his bathtub, but… 

They were smaller. 

Not necessarily by a lot, but they did seem much closer to a “human” size. 

What the hell? 

It felt ridiculous, but Hakuji found himself on a goddamn Wikipedia page of all places. 

Which only confirmed that merfolk were not that big, with the largest recorded mer being about eight and a half feet long. 

What the fuck was in his goddamn bathtub!? Some giant freak of nature? 

He stood in the kitchen doorway for about twenty minutes, reading further, digging deeper and deeper into the article. 

He sucked in a sharp breath when he read that merfolk were not to be confused with some long latin name he didn’t bother trying to pronounce, even in his head, but were commonly referred to as sirens. 

“Oh, motherfucking shit,” Hakuji breathed as he clicked on the link. 

Sirens were practically dinosaurs, weren’t they? Hakuji thought they were extinct. Wasn’t that the general consensus regarding them? 

It didn’t take reading far into that particular Wikipedia article to have that confirmed. There hadn’t been a siren sighting since the fifties. Oh sure, there were some debated sightings, discussions over whether it was a mer or a siren that was caught in a grainy photograph or blurry video. 

However, nothing confirmed. 

Forgetting about making himself lunch, Hakuji crept back to the bathroom to peer around the door and stare at the creature flopped into his bathtub. He still wasn’t awake, but surely… surely he was some kind of mer and not a siren. 

Hakuji hadn’t been stupid enough to drag back an extinct species that was apparently known for being larger and more aggressive than their mer cousins. 

He read a paragraph of the article, before his gaze flicked back to the mer to watch him for a few seconds. He read another paragraph, and repeated. 

There was so little information about merfolk. There was even less information about sirens. Neither one of them had been easily studied or maintained a close or overly positive relationship with humans at any point in history. 

No one was quite sure about all the differences between merfolk and sirens, but the main way of telling them apart physically were sirens’ larger size, as well as dorsal spines that merfolk did not have. 

Well, this creature, whatever it may be, was certainly larger than a mer. 

Hakuji hadn’t paid much attention to his back, and most of it had been covered by his wild hair while he laid on the beach. 

He took a deep breath, and crept towards the bathtub. Shooting the creature one more wary glance to make sure he wasn’t waking up anytime soon, Hakuji reached around his body, and placed a hand against his back. He slid it across cool skin until he found his spine, and his fingers brushed against the fins protruding from his back. 

Shit. Shit, shit, shit, shit. 

Hakuji jerked back and put much more distance between them. He pressed his hands to his face and let out a long, low groan. 

Why did he do this? What the fuck was wrong with him? 

Why didn’t he just leave it? Why didn’t he just call a standard emergency line and let them figure it out? 

Well… Hakuji could still do that, couldn’t he? What was stopping him from just calling the authorities? Sure, he’d have to deal with some questions he didn’t want to answer about the mer being in his fucking house, but this situation would probably be over with by the end of the day, and it would just be a stupid, weird, inconvenient thing to complain about to Gyutaro and Daki on Monday morning. 

Lingering in the bathroom doorway, he stared at his phone. 

Call. Just call. Just fucking call. This wasn’t his damn problem, and he had enough shit to deal with. 

He switched back to his browser tab instead. 

Sirens in captivity. 

Given how injured he was, and the fact that Hakuji had made the decision to stitch over his gills, if this siren was taken to some kind of facility, would they ever let him go back to the ocean? Especially considering sirens were supposedly extinct? 

And that was if he wasn’t just immediately tossed back into the ocean to die. 

Merfolk weren’t kept in captivity anymore. Never mind their reclusive nature, too many studies in the past several decades indicated they had intelligence on par with humans. Most countries had laws against it. 

Sirens had vanished before those laws were passed. 

Hakuji’s grimace only deepened as he read. 

Nearly every instance of a siren being kept in captivity ended with either the siren attacking a human, or finding some way to kill themselves. 

Granted, none of this had happened in nearly a century due to sirens practically vanishing, but Hakuji doubted things would be any different now. 

If sirens and merfolk really were some kind of intense blend of human intelligence and animal instinct, yeah, Hakuji could understand why being kept in a tank would drive them to that type of insanity. 

Which… shit, if they were really comparable to people, was it fair to even make a decision like this without… asking him? 

But fuck, could they even communicate? There was no way in hell a fucking fish knew Japanese! And it wasn’t like Hakuji would ask a person who was bleeding out if they wanted him to get them to the ER. He would just fucking do it! 

It didn’t matter how many articles he found. None of them offered the simple answer he wanted. Hell, given how old a lot of the information was, how reliable was it really? Not to mention how some of the articles he read contradicted each other. 

Hakuji tore his attention away from his phone to stare at the siren. Even with how big and unusual he looked, like this, with fresh stitches, blood stains, and unconscious, he just looked like he needed help. This wasn’t a rare, dangerous creature that humans couldn’t even begin to understand, he was just… 

Some unlucky bastard who washed up on a beach. 

And Hakuji was the dumbass who picked him up. 

He’d dug himself this hole, hadn’t he? Why should he pawn off this siren onto people who also didn’t know shit about them, and might do god knew what with him? 

God, he could practically hear Keizo lecturing him about taking responsibility for the stupid bullshit he pulled. 

True, that was normally about getting into fights, not dragging home supposedly extinct ocean monsters, but… 

Nothing good had ever come from any situation where Hakuji had ended up involved with the authorities… Sirens supposedly killed themselves in captivity. 

He couldn’t be responsible for that. Hakuji just couldn’t be. 

There was no one to call. He couldn’t trust that turning this siren over to any kind of official organization wouldn’t end in his death, just a little further down the line. 

Hakuji sighed, and stuffed his phone back into his pocket. 

Just a few days. He just had to keep this siren for a few days. Just long enough to remove the stitches, and then drag him back to the ocean, because surely he’d be okay from there, right? He would do what research he could, try and keep him as comfortable as possible, and then get him back where he belonged. 

No one needed to know, and then this siren could get on with his life as he would have. 

Hakuji could, too. 

It was fine. It didn’t need to be a big deal. Just a siren… in his bathtub… for a few days. Worst thing that happened would be getting mauled by a giant fish, right? 

Hakuji squeezed his eyes shut. 

Yeah. 

He was a dumbass for this.