Chapter Text
Normally, Izuku made an honest effort to keep her work life and personal life separate. But on this Saturday evening, as she waited for her adviser to email her, she could think of nothing else. She was nursing her twenty-third nervous mug of green tea, her voice was hoarse from muttering and worrying aloud at herself for hours, and if she paced any more laps around her tiny coffee table she was going to burn a hole right through her carpet.
Past eleven at night, as she lay wide awake in bed, as a winter storm blew fistfuls of snow at her bedroom window, her work laptop finally, finally dinged with a new email. She stopped pretending to be sleeping, snatched up her laptop, and stared at her login screen in the dark.
She’d been waiting all day, literally all day, for this email. But it still took her several more heartbeats, each one hammering loudly in her ears, before she could coax her fingers into unlocking her screen.
The email was short and to-the-point, typical of her adviser:
> Aizawa: He’s stable. He’ll heal.
Izuku took a deep, deep, deep breath. Then she tossed her laptop to the side. She leapt out of bed, twirled on her toes, and let out a sleep-deprived, stressed-for-too-long, too-much-green-tea-fueled whoop that was even louder than the one she’d let out after submitting her Ph.D dissertation.
This was big. This was huge. This was a successfully rescued coral mer, the rarest of all known mer species – only the third coral mer ever rescued in all of Japan, and only the seventh coral mer rescued, ever, for the entire world.
Yes, this, this, was half a year’s hard and painful work come to fruition. This was laughing in the face of every cold-hearted poacher, casual polluter, and careless boater that had forced this intelligent, beautiful species to dwindle into almost nothing.
This was a chance, a real chance, to help save the coral mer species.
That was already plenty to celebrate. But for Izuku, there was even more. She’d have access to so much unprecedented data from this rescued mer – behavioral tendencies, diet, rut patterns, mating, interactions with humans – so much data that she could analyze up close and personal.
She had a new research subject, now. She grinned into the darkness.
Tomorrow couldn’t come fast enough.
She spent the rest of the night – morning? – forgoing sleep altogether. She switched on her lamp, cracked her knuckles, and solidified her initial research plans: metrics and measurements, weight and lengths and sizes, photos she needed to take, scans she needed to make…
By the time she put her notebook down and closed her laptop, it was 4:52 in the morning, and… sure, yeah, that was a reasonable enough time to head into the office.
She caught the 5:30 train to the harbor, still grinning from ear to ear. A few early passengers in outfits ranging from suits to safety vests shot dirty looks at her million-watt smile from across the isle. She paid them no mind, just turned her smile toward the window instead.
The first hint of dawn brightened the sky from inky black to stormy black-blue. Despite the snow blanketing the ground from last night’s storm, the Musutafu harbor was already bustling, the pier already teeming with sailors and fisherfolk.
The train slowed as it neared the harbor station, and the Musutafu National Aquarium and Marine Conservation Center came into view, glittering even in just the morning streetlights. Izuku hopped off the train and had to mentally restrain herself from skipping the rest of the way there.
The aquarium was still closed to the general public at this early hour, so she badged her way through an employee side door. She greeted Mr. Kimura at the security desk with a cheery wave, and then she followed the halls to the medic ward. The path felt almost like a space-walk on the ocean floor, thanks to the aquarium’s décor: dark carpets, blue shades of paint on the walls, framed fossils and photos of undersea life. The whale skeleton hanging above the entrance hall drew shadowy stripes across her skin as she passed beneath it, while a trail of dangling mock jellyfish led her way to the medic ward.
The mer ward – the ward under her charge, now – was the aquarium's newest pride and joy, a true marvel in the making. She was inwardly bouncing on the tips of her toes at the thought of releasing the rescued mer into his new tank there, seeing him explore it and hopefully like it... but for now, she walked right past the mer ward and headed straight to the medic rooms.
She badged into the medic lounge, and found Professor Aizawa, her long-time adviser, sitting in one of the cozy armchairs. Ignoring any academic decorum whatsoever at this hour, he’d thrown on a faded ‘UA University’ t-shirt and a winter coat over pajama bottoms splattered with chubby kittens, and he was nursing a cup of coffee so strong Izuku could smell it from the door.
He probably wouldn’t look particularly excited – or awake, for that matter – to typical passerby. But there was a glint in his tired eyes that told Izuku just how thrilled he really was.
“Good Morning!!” Izuku greeted him.
“Mm,” he grumbled, in response. Before she could ask, he added, “Medics are still with him now. They’ll let you in, in a bit.”
She shifted her weight from foot to foot. “How long is a ‘bit’?”
“Hells if I know,” was his illuminating answer. “I’m not that kind of doctor.” He jerked his head to the mini-kitchen area, where an open box of donuts and a bag of bagels still had some decent selections left. “Take a seat. Eat something. Hydrate.”
She was too keyed up to even try to eat anything right now, but she forced herself to grab a bagel, and she brewed her twenty-fourth cup of green tea in the past twenty-four hours with the well-used coffee maker on the counter. She sat down at a table with her makeshift breakfast and pulled her work laptop from her bag. More out of habit than anything else – it was hard to focus on anything other than the fact that the rescued mer was only a few rooms away.
Aizawa squinted his one good eye at her over the rim of his mug. “Close the laptop, Midoriya. You’ve already done more than enough.”
Warmth spread through Izuku at the high praise. Aizawa had been her adviser since she’d first started on this path – first in undergrad, as an external adviser, then as her PhD adviser in grad school at UA University. He’d listened to her crazy ideas in grad school, to her wild theories on how they could infer mer migration routes from the sparse data they had, use those routes to get ahead of the poachers and pollution that had ravaged the species. He’d vouched for her, later, when she’d published her analysis in her final PhD thesis chapter. He’d stood by her when she presented her maps and her predicted migration routes to other merologists, and he’d supported her when she’d petitioned to this aquarium to hire her as a mer handler if her routes were a success.
“It wasn’t me, really,” Izuku admitted. “It was the medics, and the transport team that brought him here in the first place, and the technicians who found the poachers, and the boat crew for – ”
“It’s too early to weed through your humility,” Aizawa cut in, as the door creaked open.
One of the aquarium’s lead medics, Dr. Yamaya, stepped into the room and made a beeline for the donuts. “Evening,” she greeted them.
“Morning, now,” Aizawa corrected her.
She made a face at that. “Still evening for me. He's ready for your tests,” she added to Izuku, selecting a donut smothered in pink sprinkles. “We’ll be keeping him in the medic room for a while longer. You've got until 7 before we fill his pool.”
So a solid hour, then. “Thank you, Doctor!” Izuku told her, and barely remembered to wave to her adviser before she was out the door.
She power-walked down the hall as swiftly as physically possible without breaking any hallway rules, and then she badged her way into Medic Room D3.
The medic room was lined with workstations, medical scanners, and labeled cupboards and drawers packed with shiny equipment. Stainless steel surfaces, polished to a crisp shine, winked from every side of the room, and the hum of very powerful electronics supplied steady background noise. A couple of medics were leaning against a workstation in the back of the room, murmuring to each other in quiet voices. They greeted Izuku when she walked in, and Izuku diverted her focus just enough to respond in turn before she zeroed in on the centerpiece of the room.
There was a shallow medic pool embedded into the central ground, currently drained of all water and set up with a temporary surgical table.
And there, she got a first look at her new charge.
He was long, some 2.5 meters at least from her quick scan. He had a sharp face and a sharper jaw, pale skin, a cloud of spiky hair that was a ghostly shade of pale gold, and a bare chest with toned abs and arms rippling with lean muscle.
From the waist up, he looked almost human. Almost. But there were traits even in his upper half that were ethereal: the whisker-thin fronds mixed into his hair, so pale they were almost white; the small ear fins that fanned out over his ears, translucent and ribbed like a koi’s fin; the thin webbing between his fingers and the gills in his neck. Ruffled folds along his back marked his dorsal fin, folded down out of the way for now. There was no visible white in his eyes, and his irises were a shade she'd never seen in a human before: blood-red, like brilliant rubies.
Below the waist, he was another creature entirely. The skin around his waist itself was ridged by a thin black crest, thicker along his sides. Below that crest, skin gave way to his mer tail. It was obvious even at a glance how powerful his tail was. The entirety of it was covered in smooth black scales, which gleamed in the light like black lacquer.
As a coral mer, all of his fins were works of art, but his tail fin especially was a masterpiece: black skeletal spines connected by translucent ribbing, as strong as a dolphin’s but as pretty as a parrotfish’s. The ribbing was black at the base, and then transitioned through a gradient of vertically striated reds and golds. At the very end of his tail, the colors faded into bright white.
Izuku followed his body with her eyes, from head to tail and back again. None of her scientific jargon could do him justice, really. He was… beautiful. Simply beautiful.
Beautiful and deadly. He was covered in scars – claw marks above his waistline, old cuts along his arms, a deep nick in his right ear fin, a vicious bite to his side… and of course, the newest scar: a giant wound carved down his tail by the poacher’s harpoon, sown together and bandaged now by their medics but still marked by broken scale.
All a testament to how vicious of a fighter he must be. This mer was a survivor, and judging from the old wounds scattered across his body, he’d fought hard to keep that rare title.
The medics still had him securely strapped and cabled to the surgical table, to keep him from dislodging the splint on his tail or ripping any of his stitching. They would fill the medic pool with water and simulate a flowing current for him later this morning, and eventually they would loosen his restraints once his tail had healed more, but for now he couldn’t move an inch.
His red eyes shifted up to her the moment she entered his field of view, and those eyes tracked her as she neared the pool. He wasn’t trying to escape his bonds, meaning that he was smart enough to understand just how trapped he was. But the dangerous glint in his eyes told her that if he wasn’t restrained right now, he’d have long since ripped all of their throats out.
She walked to the front of his pool at an exaggeratedly sluggish pace, careful to stay in his direct line of eyeshot, and then lowered herself over the side. She set her laptop and backpack on the dry floor of the pool, and then she slowly, slowly approached his head.
He watched her approach, unblinking. His ear fins flared out and rattled against his ears, a clear warning. The scales of his tail turned a dark shade of red around their edges, almost like they were burning. She didn’t know this mer at all to know what emotions this particular color was signaling, but she could make a wild guess that red meant he wasn’t pleased she was coming so close.
“Easy,” she murmured, even though there was no way he could understand her. Yet. “I just need to be close enough to sync with your translator…”
The medic team had already clipped the little device behind his right ear fin on her behalf, following her instructions. It wasn’t an invasive device – he could unclip it himself, if he wanted to, once his hands were free – but it was secure enough that it wouldn’t fall off otherwise.
She pulled out her phone, opened up the app she’d helped design back in grad school, turned on Bluetooth – and was relieved to see two entries pop up on her screen, one from his translator and one from the translator clipped in her own right ear. She waited as the app updated both devices’ software and connected them.
Fingers crossed that all coral mer in this region spoke the same language, let alone the same dialect. She made sure to start small. “Hello?” She tried.
The mer froze, ear fins stilling. His eyes widened like sand dollars.
“Okay, you’re clearly hearing something,” she said, and had to fight to keep her voice from rising in her excitement. “Can you… can you understand me?”
The mer flinched, head trying and failing to tilt away from the translator in his ear, arms jerking against his restraints. The red edge to his scales soured into a sickly shade of yellow.
Okay, so he was freaking out a little bit. That was fair. “This is called a translator,” she explained to him, tapping the device in her own ear. “It takes what I say, translates it, and then it says it again in your ear in your own language. I worked with a couple of coral mers, like you, before I came here. We trained a language model to… oh, you’re not going to understand what that means at all.” She frowned. “Well, basically we learned your language, how it maps to ours, and now, in a way, we’ve put our languages in these translators.”
His gaze drifted to her translator, and Izuku dared hope that this was working, that even if he wasn’t following the full conversation, he at least understood the words his translator was murmuring in his ear.
“You’ve just survived a poacher attack,” she went on, speaking as clearly as she could. “Poachers are… they’re basically humans who capture and kill mers, and sell them for parts. I hate that this is true, but there are humans out there who really, really like mer scales, coral mer scales especially, and they’ll pay a fortune to have jewelry or clothes or medicine made from them. We’ve been on the lookout for any signs of poachers on the coasts, and we heard a tip about some spotted farther south. The police captured the poachers, and they confessed that they’d attacked you, and tried to capture you.” Her gaze strayed to the bandaged gash on his tail. “I don’t know how you got away from the poachers in the first place, but thank goodness you did. Our rescue team combed the waters, and eventually they found you, hiding inside of an old shipwreck and bleeding out. They brought you back here, healed you up, and now here we are.” She beamed at him. “Long story short: we’re not here to hurt you. We’re the good guys.”
Silence greeted her little speech. But the sickly yellow of his tail scales had faded back to black as she’d spoken, and Izuku took that as yet another really good sign.
She shifted back to the basics. “My name is Izuku,” she said, gesturing to herself. “I’m a marine biologist – a merologist, specifically, someone who studies mers. I focus on data analysis. Izuku,” she repeated, more carefully. “What's your name?”
He didn’t answer her – just squinted at the phone still in her hand, as if glaring at it would force it to spill all of its secrets.
“If you don't tell me your name,” she warned, “I get the right to make one up for you.”
No response.
“Ohhhkay,” she mused. “How about… something cool, like Nightshade?”
She was starting to worry that he wasn’t comprehending any of what she was saying after all… but then he shot her a look, which told her 1) he understood exactly what she was saying and 2) he did not think Nightshade was as cool a name as she did.
She was outright grinning now. She’d only worked with two coral mers before, back during her PhD, and already he was proving feistier than those two mers put together. “What about Trident, maybe? Trident's a cool mer name.”
His lips drew back in a silent grimace, revealing two rows of wickedly sharp teeth, before he went back to pointedly ignoring her. An impressive feat, considering how there was nowhere else for him to look, really, let alone go.
“Hey,” she reassured him, dropping her voice a little. “We just want to help. We want to get your tail healed up all the way, and we want to kick all of the poachers off this planet, and we want to revive your species. We’re not going to hurt you, I swear we aren’t. We want to help you recover, and then we want to help your species recover. That’s all.”
He searched her face for a long, long moment.
She held his gaze, graced him with her gentlest smile.
Finally, he opened his mouth, and he spoke. His voice was deep enough that it almost rumbled, and it was overlain with something faintly musical, like bass notes, and further undercut by a series of dolphin-like clicks.
[Translation unavailable], her translator piped into her ear.
Oh, gods. Maybe he did speak a different dialect. “What did you say?”
He spoke again, a growl this time.
[My name], her translator told her, and she felt a little thrill at these words she could understand. [It’s – ], and he made that same complicated rasping melody.
Her translator stuttered through a few syllables, before it gave up. [Translation unavailable].
She took the translator off altogether. “One more time. Slowly.”
With a glare that could have seared raw meat, he repeated the lilting noises.
Izuku focused on the tones, the syllables above the clicks. “Kah... tsssuuu... kiii,” she tried to emulate, slipping the translator back on.
[The fuck], he snapped. [That's not what I said at all.]
A real sentence, fully converted by her translator, and even with the coarser language accurately captured. Izuku was smiling so hard now her cheeks were starting to hurt. “Sorry, my throat can't make the same clicks and notes like you can. Katsuki is the best I can do, in my language.” After a beat, she smiled even more. “But I really like it. Much better than Trident.”
He just clicked his teeth in response.
“It's nice to meet you, Katsuki,” she told him, sincerely. “And again, I’m Izuku. I-zu-ku.”
The expression on his face said he didn’t give a shit what her name was.
Even so. This was an enormous amount of progress already.
She straightened up and went to fetch her backpack from the floor, talking all the while. “I'm going to run some tests, okay? Nothing that'll hurt, just measurements and some scans. And I’ll walk you through exactly what I’m doing as I do it.”
This room was outfitted with scanners, and even the surgical table he was strapped to was calibrated to give weight estimates. She pulled out some of her own low-tech tools from her bag: measuring tape, camera, notebook, pen. All very rudimentary, but effective. Then she snapped on a pair of medical gloves and got to work.
She showed and explained each tool before she used it. “This is a length of measuring tape,” she'd say, “and I'll use it to measure the length of your tail,” or, “this is a camera, so I can take a photo of you.” She paused after every measurement to jot down notes in her notebook, or to load photos and data tables on her laptop.
There were still medics in the background of the room, but a few minutes in and Izuku forgot all about them. Her world shrank to just her and Katsuki. She let herself really slip into a rhythm, and soon she wasn't just dictating for his benefit but also for herself, muttering measurements and ideas under her breath, questioning aloud the strength of his tail, debating with herself the reasons for his fin colors, writing entire sections out loud on how his scale pattern differed from Miu's…
She kept a careful distance and stayed within his field of view as much as she could. She didn’t touch him, but damn did she want to. Chalk it up to whatever foolish impulse made humans want to pet wild tigers and tame feral wolves, but she really wanted to reach out to him, feel the exact texture of his scales, his fins, his fronds.
Miu, one of the two coral mers she’d worked with back in grad school, had loved being petted. Miu used to flip upside down like an otter by the handler dock of her tank, and wiggle around, literally begging to be petted. She’d made little murr sounds whenever Izuku or another handler had stroked her tail, and she’d squealed like a kitten whenever they tickled her stomach. But Miu had grown up in tranquil captivity. It had been just Miu and her elderly mother living in that conservation tank together, with no predatorial or territorial threats in the slightest.
Well, other than the vague danger of Izuku and the other doting handlers spoiling the two mers to death, anyway.
Katsuki was not that. Katsuki was full-blown apex alpha predator. Katsuki was wild, through and through.
So Izuku didn’t touch him. But she ran her gaze again and again over his form, and she took way more pictures than she needed to.
She flipped through her photos and tables, used some of the really fancy equipment in the room to run some scans. She reviewed her output, retook a few measurements, jotted more logs in her notebook.
She was just triple-checking the last files on her laptop when her timer dinged on her phone.
Right on time.
“That's my cue.” She was sitting cross-legged on the tank floor at this point, so she set her laptop aside and stretched until her back cracked. “Thanks for being so good, Katsuki.”
He just blinked at her, slowly. He hadn't said one new word to her, not since he’d told her his name. He also hadn’t looked away from her since then, not once.
“All my tests are done,” she murmured into the quiet, just as the door creaked open and more medics trickled in. She stood up to leave, and favored him with one last smile. “Shame, really. I'm not done examining you at all.”