Chapter Text
The medics kept Katsuki confined to the medic ward for several more days while his tail finished healing. Izuku spent those days alternating between setting up the aquarium’s brand-new mer exhibit and furiously cranking out figures from the data she’d already gathered from Katsuki.
She emailed a PDF crammed with draft plots to her adviser Aizawa, who’d returned to his post at UA University. He responded with several short-but-approving comments, some brief suggestions, and one note that instructed her simply to ‘Breathe’.
Breathing evenly was kind of hard, though, when she was so excited. Because this was exciting!! This wasn’t just an empty tank and a wistful dream, anymore. They were really here, now – really helping to bring this smart, beautiful, enigmatic mer species back from the brink of near-extinction.
On a snowy Friday those several days later, the medics announced they were ready to release Katsuki into his new tank. Izuku had to physically remind herself to breathe, then, to avoid passing out.
The gigantic new mer ward spanned three entire floors of the aquarium, from Floor-1 at ground level down to Floor-B2 in the basement. The mer tank took up the vast majority of that space, and was designed like a tropical undersea paradise: there were rock spurs and outcrops with sandy shores both above and below the water, saltwater fish and squid and eel that provided plenty of food for Katsuki to hunt, and a rainbow of coral and seagrasses blooming an entire forest across the sandy floor.
From a birds-eye view, the tank was shaped a bit like an ‘E’ that had been stepped on and squashed, so there wasn’t much space between the horizontal prongs. The top horizontal prong of the ‘E’ was the gallery section of the tank, which interfaced with the mer exhibit in the visitor portion of the aquarium. Once Katsuki’s exhibit was open, visitors would be able to see him swim past all three floors’ worth of glass.
The middle prong of the ‘E’ was the cove section of his tank, and was completely isolated from handlers and aquarium visitors. That entire prong simulated a private sea grotto, featuring lush skylights, naturally heated water, and a briny bay.
The final, bottom horizontal prong formed the handler section of the tank, which Izuku and any other handlers could access directly via a gated dock. The handler office – Izuku’s new office – sat on the staff side of that gate, along with a landing platform.
Izuku set up shop in the office, and then she wheeled her office chair right up to the back wall, a floor-to-ceiling window that offered a glorious view down into the handler section of his tank. She ogled through the glass as the medics brought Katsuki in, lowered him into the water, and finally, finally, removed his restraints.
Katsuki unfurled his dorsal fin, a gorgeous black-spined work of art with gold-red-white ribbing that cut through the water like a sail. With a powerful flick of his tail, he dove down, until he was no more than a dark shadow flitting beneath the surface.
Erin, Izuku’s backup handler, leaned a hip against the glass beside her. Erin normally worked in the dolphin ward of the aquarium, but she’d volunteered to fill in for Izuku here in the mer ward during emergencies. “Damn, he’s fast,” she noted.
“Mmm,” Izuku agreed, not taking her eyes off of that swimming shadow. She tracked Katsuki until he swam too deep for her to see him properly from the surface, and then she wheeled her chair back over to her desk, pulled up the surveillance cameras scattered across his tank on her monitor, and cracked open a notebook.
Erin followed her and whistled at the screen over her shoulder. “Look at him go…”
Oh, Izuku was looking alright. She couldn’t look away.
At first Katsuki flitted past the cameras so quickly she could barely register him at all. But many, many minutes later, he slowed. He explored each section of the tank thoroughly, darting back and forth like a hummingbird. One minute he was at the tank bottom, hovering over the forest of coral. The next minute, he was in the gallery section, staring through the glass out into the empty exhibit on Floor-B1. He stuck his head above the surface in the handler section and spent the longest stretch yet surveying the tank walls, the handler dock, the gate that was out of his reach.
Erin stepped away, eventually, to return to the dolphins, but Izuku stayed rooted in her chair. She filled her next few notebook pages with quick sketches, notes on his swimming pattern, his initial behaviors in unknown waters. He was fascinating. And already she could tell, from the way he didn’t try to leap onto the handler dock but he did try to jimmy open one of the tank vents with a broken length of coral, that he was very, very clever.
But as much as she wanted to spend the rest of the day studying Katsuki, that was only half of her job here at the aquarium. The other half of her job was running the aquarium’s brand-new mer exhibit.
So she unglued herself from the monitor, left the office, and marched out to the exhibit.
The exhibit was scheduled to open to its very first crowds in just a few days, and so today, Izuku was going to not freak out about that, and instead she was going to do a meticulous review of every informative mini-station she’d set up.
She was just rereading her info plaques in the ‘Mers: Myth to Modern Marvel’ mini-station on Floor-B2, checking for the thousandth time for any typos, when she felt the hairs rise along the back of her neck. It was that simple sensation, some buried survival instinct, perhaps, that had her absently glancing over her shoulder.
Her heart jumped in her throat at the sudden sight of Katsuki, in all of his clawed, sharp-toothed, 2.5+ meter-long glory, right behind his tank glass, hovering within a tall cluster of kelp like a tiger crouching in the undergrowth. His bright red eyes almost shone against the dark green stalks.
Izuku blinked at him, rapidly. Once she got over the initial shock that an apex predator had been watching her from the shadows, she scrambled to grab her translator from her jacket pocket. She clipped it on and switched on the mic. “Hi!”
He flinched, scale-edges flashing that sour shade of yellow, and raised one webbed hand to his ear.
“Oh, sorry, sorry,” she told him, quickly. “Didn’t mean to startle you… you startled me first, though.” Pointing at her ear, she explained: “These translators work anywhere, not just when we’re next to each other. Oh, and there’s a button at the top that lets you turn your mic on or off – right up here. Yours should still be on. But just in case you accidentally press it or something, that’s how you turn it back on.”
He absorbed this for a few seconds. He raised a hand and, very pointedly, pressed the button on his translator, turning his mic off. Then he swam several meters away, and peered through the glass at her ‘How You Can Help!’ mini-station instead.
Well, that dashed Izuku’s hopes of getting to know him better. Not that she’d expected him to talk or want to be friendly with her, but… she’d kind of hoped.
So she went back to her thorough scrutiny of her mini-stations. She checked again and again that the hanging photos weren’t crooked and the skeletal replicas weren’t chipped, that her info cards were devoid of unexplained jargon and the plaques had a clear narrative, reviewing and re-reviewing and re-re-reviewing, because the thought of all the exhibit’s very-first visitors on Wednesday learning absolutely nothing or leaving bored out of their minds or gods-forbid rooting for the poachers was giving her nightmares, and –
She was right in the midst of muttering under her breath over the exact placement of the large decorative stuffed turtle relative to the smaller decorative stuffed turtle on one of her ‘Ask a Merologist’ booth desks, and, okay, maybe she was starting to freak out a little, and maybe she needed a break.
So she forced herself to sit down on a Floor-B1 bench with her water bottle and sucked in deep breaths like they were part of a mantra.
Katsuki drifted down from Floor-1 into her view. He’d been a flickering shadow to her this whole time, flitting back and forth between Floor-1 and Floor-B2 just like she was, squinting at her colorful exhibits over her shoulder while she fussed over them. He stared hard at her through the glass, gaze as strong and sharp as a spear.
Izuku was suddenly very conscious of how her curly hair was spilling messily out of her already-messy bun, and of the dried sweat staining her aquarium work shirt from all the times she’d foregone the elevator and dashed the stairs between floors.
She sipped at her water, eyes and mind wandering over his scars. He had to be full of stories about them, and there was that particularly nasty set of curved claw marks that was probably worth a whole novel, she couldn’t even imagine what kind of creature had made those –
[Oi. Dots.]
It took her a second to realize Katsuki was talking. To her.
It took her another second to realize she’d been muttering. Again.
Smiling wryly at herself, she reached for her translator to turn her mic on –
And registered, belatedly, that it was… already on. Which meant she’d been bombarding Katsuki with her absent muttering since she’d last spoken to him this morning.
Damn. She lowered her hand. “Dots,” she echoed.
[You’re covered in them.]
Izuku could only tilt her head at that, before it finally clicked. “Oh…” She held out her arm. “These are called freckles. And my name’s Izuku. I-zu-ku.”
[Don't give a shark-shit,] was his immediate response. [What're you keeping me in here for?]
She rubbed a hand behind her neck, further dislodging her messy bun, and tried to distill the struggles of conserving a critically endangered species into a couple of sentences. “Well… there aren’t many of your species left. Coral mers, I mean. Mers are really rare already, but coral mers are… almost gone. So we’re keeping you here to help protect you from poachers, and other threats.” She bit her lip, and then added, “And we’re also really, really hoping you’ll help us keep your species going.”
His ear fins twitched as he thought this over.
She took another sip of water as he processed, and waited for him to ask the obvious follow-ups, the ‘what’s, the ‘how’s.
[So you're keeping me here to mate a mermaid,] he said, finally.
Izuku almost dropped her water bottle, because that was not a logical leap she’d expected him to make on his own. She strained to come up with a better, kinder way to phrase that particular objective of her job here, before she just sighed. “Yeah… yeah, we are.”
She'd expected him to growl or snap at her – a warranted response, frankly – but to her utter surprise, she spied a new gleam of something like interest in his eyes.
“You're… not upset about that?” She asked him, more than a little stunned.
He was silent for an even longer moment. [Depends on the mermaid.]
That honesty was even more shocking than anything else he'd done so far. “Because instinctively, you want to find a mate,” she reasoned aloud. “And you should be mated by now, given your age.” She glanced at his neck – smooth, unmarked, no signs of a mating bite at all. “It’s weird that you’re not.”
Silence for a while, again. [I've been looking for a long time,] he admitted, eventually. [Haven't found anyone that I want. Not… not even many to find.] A beat. [I haven’t seen a new mer in years.]
Just the bare thought of that kind of deep isolation chilled Izuku’s blood like ice.
She set her water bottle down and pulled out her phone, glad that she could provide him with what she hoped was… some hope. She skimmed through her photos, and then she walked the phone up to his tank so he could see them. “This is Miu. She’s about your age, but she was raised in captivity. She's smart, super-nice, really kind, sweeter than candy honestly – and she’s beautiful.”
Katsuki pressed right up against the glass to better see the photos, eyes going wide.
“I think you’ll really like her,” Izuku smiled, heartened by his reaction. “Everyone likes her – it's impossible not to like her, really.”
He only grunted at that, a faint rumble in her ear. But there was no denying the curiosity in his gaze, the way he didn’t look away from her phone. [You’re bringing her here?]
“Yep.” Izuku scrolled through a few more photos, pausing on one where Miu was frolicking with a turtle. “In early spring, at the beginning of your mating season. Right when your scales first start to shine.” Lowering her phone, she went on, “Until then, it’s my job to make sure you’re happy here. I know your tank isn’t the ocean, but… it’s huge, and warm, and safe, and you’ll get live deliveries of plenty of new fish every week, and… and if there’s anything you need, anything at all, just let me know.” After a beat, she ventured, “How… how do you like it, so far?”
He frowned down at her, and then past her, to the mini-stations she’d arranged around the room. His tail fin twitched, a complicated staccato motion, like fingers tapping on a desk. [You know too much about us.]
She dared to believe that meant he liked it. “I’ll take it,” she said, with feeling. “So, is there anything else you’d like, so far? Any favorite fish? I don’t think I’ve seen you hunt anything, yet…”
His eyes narrowed into slits. [You were watching me?]
“Oh. Well, yes. That’s… also part of my job.”
[How,] he said, and the word came out less like a question and more like a threat.
“The cameras,” she admitted, gesturing to one hanging in view from a far tank wall.
He swam off to that camera without another word.
“You can't break them or take them down,” she warned him, before he could try anything. “They're locked up in industrial cages. I've seen those cages withstand full-on shark attacks. You'd break all your claws even trying.”
He twisted around in the water as he scanned the other tank walls. [They’re everywhere.]
“They're mostly for emergencies.”
[Mostly,] he echoed, drily.
“Well, I’m… I’m studying you, while you’re here. But I’m not studying the cameras anywhere in your cove,” she reassured him, quickly. “Those really are just for emergencies, just so that if something happens to you back there we’ll know.”
Unlike the caged cameras scattered across the rest of his tank, the cameras in his private cove were disguised to look like innocent rocks, so that they wouldn't disturb him.
He immediately darted off and out of her view. Going to the cove to see for himself, likely. With a rueful sigh, Izuku braced herself for the worst.
Sure enough, her phone pinged barely a couple of minutes later. She'd written some code that analyzed live footage from Katsuki's cameras, and marked any blips – i.e., Katsuki – for her analysis, and to catch any emergencies. The fact that her phone was pinging her about the footage at all meant something very, very significant had blipped, big enough in scale to possibly be an emergency.
She pulled up the surveillance footage from his tank on her phone. At once, she noticed all of the cove cameras had gone completely dark. Biting her lip, she rewound the footage, restarted it… and watched as a very determined Katsuki swam every inch of his cove. His face popped up in front of one of the hidden cameras. Eyes shining in triumph, he reached for the camera, twisted it – and now that camera was watching nothing but the rock wall.
Damn. “Okay, Katsuki,” she grumbled. “Now you’re being a little too clever.”
At that, he outright laughed at her… and it was far more of a sound than any human could make. Katsuki’s laugh was a deep burst of laughter, a trill along a musical scale, and pebbles in a riverbed, all rolled into one low melody.
[Translation unavailable], her translator reported, speaking over the sound.
He was laughing at her, clearly, but Izuku couldn’t even be bothered by that. She was too caught up in the complex tones of the sound. “Turn them back around,” she tried. “Please?”
[Eat shark-shit, Freckles,] he said, still chuckling – and then there was a click, a loss of background static, as his mic switched off.
Izuku just blinked down at her phone screen.
Freckles, he’d called her.
There was nothing she could do about the cove cameras, short of getting in the tank herself to fix them, and obviously that wasn't going to happen. But she couldn’t even be all that mad or worried about them right now. Not when the curious notes of his laughter were still ringing in her ears.
Now that he knew about Miu, Katsuki seemed quite interested in meeting her, and willing to live peacefully in the tank until then. He’d stopped trying to crack open the tank vents, at the very least.
But mating season was still some weeks away, and in the meantime Katsuki would be spending his time in this giant tank alone. As Katsuki’s handler, Izuku’s job was to make sure he was healthy and happy, and a lot of that stemmed from him not being bored. This wasn’t going to be as simple a task as throwing some blow-up balls and rings into the water, though. He needed much more complex stimulation than that.
He wasn’t like Miu, back in grad school. Another handler had once taught Miu how to knit, and Miu had then had an absolute blast knitting a whole ocean’s worth of sea creatures, which she’d decorated her and her mother’s tank with and had given to her handlers as cute little gifts.
Unfortunately, Izuku doubted that untamed apex predator Katsuki would take well to knitting.
No, Katsuki was a predator, through and through, and he needed activities that would hone his territorial, hunter, and competitive edges.
So the next morning, Izuku came into the handler section of his tank with a crate full of ideas. She crossed the landing platform, passed through the gate, and stepped out onto the handler dock.
She was careful to mind the dock edge as she walked. Katsuki couldn’t get onto the dock proper without painfully beaching himself, and he was clearly smart enough to realize that – but he could reach over the dock’s edges. Mers were intelligent and beautiful and fascinating, yes, but they were also dangerous. Izuku had heard enough reports from other countries about more common types of mers attacking, killing, and even eating sailors out in deep waters. So Izuku had long since put down bright yellow caution tape within the handler dock’s perimeter, to make sure no handlers accidentally stepped into his reach.
She stayed very clear of those yellow caution lines as she sat down near the end of the dock. She slipped on her translator and turned on her mic. “Hey, Katsuki. I have something for you.”
She heard his mic click on at the edge of her hearing. [What.]
“Come see,” she coaxed. “I have some gifts I think you’ll like.”
[Doubtful,] was his wry response. But a little later, as she was pulling items out of the crate and setting them up on the dock, his dark shape rippled beneath the water.
He came right up to the dock, crossed his arms on the surface, and leaned toward her over the edge. [What?]
Izuku paused, one arm still buried in the crate. She could only see the top half of him right now, the mostly human part: bare chest, muscled arms, hair dripping with water. He seemed so human, almost – like this was just a pool and he was just a swimmer, come to talk with her at the edge.
Almost human. Almost.
But there were still the fronds scattered through his hair, the ear fins that were slowly flaring out the longer she just stared. And the eyes – now that he was above water and exposed to the bright lights overhead, his pupils were shrinking down to smaller round circles, the red spreading from just the barest rings around the edges into seas of vermillion around the black.
[What, Freckles,] he repeated, more loudly.
Freckles, again. Izuku had to struggle to find the thread of her thoughts. “Izuku,” she reminded him. “I brought some games for you.”
[Games], he echoed, voice dripping with even more skepticism than the water from his hair.
She gestured to the boards she’d been setting up on the dock beside her. “This one is ‘go’. And this one is ‘chess’. They’re both strategic territorial games; takes a lot of forethought and planning to win them. I’d like to teach you how to play.”
He surveyed the boards and their pieces in silence. She could already see how he was warring against the very idea of playing a game with her at all, purely on principle.
So she changed tactics. “Nevermind,” she sighed. “Most creatures can’t handle a game even close to something like these in complexity, but I figured you might be able to… guess I was wrong…”
One of his eyebrows twitched.
“I mean,” she went on, tracing a dejected finger over one of the chess queens, “I’ve never tried to teach these games to anyone, let alone a mer, but I thought you might be able to figure them out, maybe, since you seem pretty clever… ah, well. Guess I’ll just pack these back up…”
[Stop that,] he huffed. [I know what you’re doing.]
“Oh.” She was fighting to keep a straight face at this point. “You do?”
[I’m not a dumbass guppy,] he snipped. [And you’re not subtle.]
“Well…” She picked up the chess queen and twisted it in her fingers. “Since you’re not a dumbass guppy,” she mused, placing the queen at the edge of the caution tape, “guess you’d know why you should give this a try.”
He tilted his head to the side, brow furrowing.
“And if you win,” she went on, sweetening the pot, “I’ll give you a prize.” She paused for dramatic effect, and then she added in a lower voice: “A Human Thing. Like these.” She pulled the final treasure from her aquarium jacket pocket: five jumbo-sized paper clips, each a shade of rainbow, which she’d taken the creative liberty to link together into a chain. She swung the chain over the chess board like a pendulum. “I’ve seen how crafty mers can be. Bet you could do something really cool with some of these.”
Oh, she had him now – there was an actual gleam in his eyes as they tracked the swaying chain.
“So.” She tucked the chain back into her pocket. “What d’you think?”
He appraised her for a long moment, scrutinizing her just as carefully as he’d scrutinized the game pieces just before.
She held his gaze, feeling for that moment like she was being X-rayed. She registered, abruptly, how there was only the caution tape zone between them, and how she could feel her own heartbeat faintly in her ears.
Mers have exceptional senses of smell and hearing. Her exhibit info card on this fogged the back of her mind, unbidden.
He could probably hear her heartbeat. Something about that truth had the hairs rising on her arms.
[I’m thinking,] he said, so suddenly that she startled a little, [you’re gonna run out of Human Things. Hope you have more than just five of those, Freckles.]
“I do,” she beamed. “We’ll see if you end up needing them.”
She walked him through the mechanics of both games, the boards and the pieces, and answered his small barrage of short but sharp questions. Once he had the logistics down, she played him in a handful of test games. She was careful to only ever pass the board across the caution tape, never any part of herself. He smirked openly at her caution zone, but he did humor her enough to slide pieces into her safe reach whenever she needed them back from him.
After a few real games, where she turned off the tutorial and took the guardrails down, she had to wrap things up. “Those were some really good first attempts,” she praised him. He hadn’t won any, but he already played like someone who would win, given practice.
He’d been toying with his chess king piece as he studied the board of his final loss, but at her words he shot her an irritated look.
“I’m being serious,” she chuckled. “I already think you’re going to be a really great player. Honestly. You just need practice. Which,” she announced, pulling some rolled-up items from her crate, “is why I brought these.” She unfurled the first roll to show off a transparent blown-up version of a go board. “The exhibit’s opening in a few days, and there’ll be tons of visitors passing through. So. I’m going to hang these boards up on our side of your tank. And I have these stickers here, see, that are waterproof, and represent all the game pieces. So if you’re ever feeling bored, you can play games with the visitors. You’ll be able to see the board on our side, and stick game pieces to the wall on your side.” She tapped the little boxes she’d filled with chess and go stickers. “It’s… it’s not perfect, but it should work.”
She put the little boxes of stickers back in the crate, snapped the lid on, and then she pushed the whole crate over the caution line and into his reach. “And this is for you, too. Lots of other stuff in there, all waterproof: puzzles, Rubik’s cubes, snap-blocks… help yourself. If you want me to explain anything, let me know. And you can keep the crate, if you’d like, put whatever you want in it.”
He grabbed the edge of the crate, and in an impressive display of both arm and tail strength, hoisted it over the dock edge and held it with him in the water. His brow was furrowed even more now than it had been over their matches.
“Oh, and here…” Izuku unlinked one of the paper clips in her pocket and slid that across the caution line as well. She favored him with a smile. “Thanks for playing with me today.”
Katsuki reached forward and picked up the paper clip, handling it as delicately as if it actually was a treasure. He didn’t say anything, but Izuku noticed a color was tinging his ear fins: a shade of dark purple, like violet. The hue was very faint, like a single drop of ink infusing a glass of water.
Izuku was slowly constructing a mental map of his emotional signatures – dark-red for anger, sour-yellow for anxiety or fear – but this violet she hadn’t seen before. Was it… embarrassment, maybe?
Before she could think any more on it, Katsuki rolled and sank into the water, leaving nothing but the barest ripples behind.
Izuku stood up, brushing off her knees. She gathered up the rolled boards and the boxes of sticker pieces for visitors, and then she headed to the exit, already mapping out how she’d set this up as a new mini-station in the Floor-B1 exhibit.
As she was passing through the dock gate, though, she caught one last snippet from her translator:
[Thanks, Freckles.]
Before his mic cut off altogether.
She clutched the boards more tightly to her chest, and she headed out to the gallery exhibit with a faint smile that no one was around to see.