Archive of Our Own

Iron coated Katsuki’s tongue. He thrashed harder, panic shocking his body into action. It just made everything worse. The sharp wires of the net dug into his skin, intending flesh and scales alike until tendrils of bright red filled the salty ocean. His throat was raw from what felt like hours of fighting. Every kick of his fins sent white hot pain ripping up his spine. Black pressed in from the edges of his vision. 

The water had been so gray this morning, reflecting the dark thunder clouds above the water’s surface. Katsuki couldn’t see the thin barrier until it was too late. Hulking metal boats that flaked deep red rust into the ocean passed above as he struggled. 

Fish had also become entangled in the barbaric trap, their eyes having long gone gray. Katsuki refused to end up like those simpletons. He was a mer. Strong, powerful…and currently in the same predicament as 50 other sea creatures. Intrusive thoughts flashed in his brain sending a jolt of panic to his heart. He thrashed again. A raw scream ripped from his throat as every nerve in his body lit up in pain. 

Well, now he’d done it! Katsuki had rolled and twisted so much that his arms were now wrapped tightly against his body, the awkward angle throbbing in his joints. He wheezed as his gills failed to provide enough oxygen. The wiry net was digging against his chest and neck. He couldn’t breathe! Katsuki thrashed again, but it only worsened his crisis. 

A booming splash echoed from above. Something had fallen into the water. The mer tried to locate the object, but he was so tightly bound, his range of movement had been reduced to almost zero. His brain was beginning to go fuzzy, body tight with tension. Something large and black danced in Katsuki’s peripherals. A wall of bubbles rose beside him and he blinked rapidly.

A glint of silver gripped in a gloved hand had the mer thrashing again. He hissed and bared his sharp teeth at the human. Goggles and a round breather hid his face. It only served to make Katsuki more defensive. He snapped at the hand holding the knife even as it began to slice the netting trapping his body.

Tight tension was released from the end of his tail. The mer kicked hard only to let out another rough scream. It hurt. Everything hurt!

“It oookaaay,” the human rasped through the breather. “Gonnna get yooou out.”

Scarlet eyes fixated on the knife. Katsuki arched away from the blade when the flat of it pressed against his stomach. The rough sawing against the tight cords of getting rocked his body harshly. His gills were still bound tight. His cells burned for oxygen. The edges of his mind began to play images. Colors of the coral from warmer waters danced in his vision. Warm, pleasant. His eyelids felt so heavy. Maybe he should just close them for a bit.

“Nooooo come on!” The human shouted through a wall of bubbles. His efforts doubled, thrashing Katsuki’s body against the current. “THERE!” 

Sharp pinpricks scraped against Katsuki’s gills. He could taste blood with every shallow breath. Something soft pressed into the small of his back, just under the spiny sailfin, and he swore it felt like he was rising. The cries of gulls echoed in the air as the roaring of waves crashed around him.

“Over here! Heeey!” A voice shouted desperately, shaking his earfin. 

Scarlet eyes cracked open to catch a glimpse of a massive white boat. Something was being lowered into the water and his body was being shoved into it. Katsuki screeched and thrashed against the rough material. His stomach dropped as he was raised out of the water, swung above half a dozen humans gazing at him.

Someone approached and Katsuki snapped, flinging out a bloodied arm in defense. 

“Woah, woah,” a human with bright yellow hair warned. “Don’t rush him.”

The deck was cold and hard against his wounds. Katsuki let out a desperate wail, claws digging and slipping against metal. He received a faceful of water and almost choked as he switched back to using his gills. His entire body was trembling against the cold liquid pouring over him. 

“Keep him restrained!” That voice from under the waves called. Vibrations shook against Katsuki’s ribs as the human rushed him. “We need to triage. Those damn haulers shouldn’t even be out here.” 

Hands pressed against the mer’s arms, pinning them to his sides. He thrashed and cried out. Katsuki’s sail extended, sharp spines pointing toward the dark sky. Hurt. He was hurt.

Green filled his vision. Sopping curls pressed against a tanned forehead that was coming closer. Katsuki reared back with a screech, teeth snapping desperately to keep the danger away. Sparkling emeralds dripped over freckled cheeks as the human fell to his knees before the mer. 

“We need to clean his wounds,” the human’s voice wavered. His hands, still wrapped in black, shook as he reached forward and maneuvered behind the mer. 

Pressure against his tail whited out Katsuki’s vision. His stomach lurched dangerously. Ringing rattled his earfins, and when his vision cleared all the humans were covering the sides of their heads. The green human’s face was scrunched in pain and Katsuki realized the overwhelming sound was coming from his own throat. 

“Come on, Gorgeous,” the human grunted. “Work with us.” 

A renewed grip tightened over Katsuki’s back and arms. His heart raced in his chest. Water continued to wash over his gills that fluttered rapidly with panic. Pain seared hot from his tail to his spine and he thrashed with a scream again.

“Hurts! Hurts!” Katsuki screeched. He felt the jolt of surprise from the hands holding tightening around his shoulders. “No! No!” Sobs wracked his frame as these humans carved him up. Would they really eat him alive? Fear seeped into every fiber of his muscles. 

“Just a b-bit more,” the green human stuttered. 

Katsuki screeched and thrashed. He swore they were chopping off his fins. Damn them! He’d seen what they did to sharks, slicing them up and tossing them back into the sea to die. Warm blood flooded around the mer’s face. This was it. They were going to throw him off the side and let him sink to the bottom. Monsters! A crack echoed against the metal, sending white hot pain across Katsuki’s nerves. His stomach emptied itself across the deck, vision blinded by immeasurable agony. 

“Izuku, wait!” The yellow human gasped as green flitted into the mer’s vision once more. 

This was his chance! With fury and fear pushing him forward, Katsuki lunged. Hot, thick blood filled his mouth the moment his teeth sunk down. A screech of pain, doubled pressure against his back and a pinch to the side of his neck. And then he felt very sleepy. The mer’s jaw went slack, teeth dragging out of freckled flesh and thick rubbery material. Katsuki’s head hit the metal ground with a thunk. Everything faded.

“Midoriya! Are you okay?” Shinsou asked, dark eyes wide with concern.

“I’m f-fine,” Izuku hissed, gripping his arm at the elbow in a makeshift tourniquet. “It was inevitable.” A short laugh bubbled in his throat. His knees were throbbing from his prolonged position on the deck. “We sh-should transport him quickly.”

Shinsou nodded. “I’ll advise Aizawa.” His rubber boots thudded and squeaked against the slippery metal, the sound fading as he climbed the narrow staircase to the helm.

Izuku leaned back with a sharp exhale, butt leaning on his heels. The mer was brilliant. The biggest one he’d ever seen in all his years studying these majestic creatures. Close to three meters with thick, corded muscle that continued to twitch even as the mer succumbed to the tranquilizer. But his tail. Tears stung in his emerald eyes as he hung his head. 

A hand rested heavy on his shoulder, offering a light squeeze of comfort. “You did good.”

“I almost didn’t make it,” Izuku sighed. “He was drowning even as I cut that awful net. The fibers were nearly invisible in the water. It’s no wonder he got caught! God, I just want to beat the shit out of all those corporate heads who claim they utilize ethical fishing practices. How the hell is that ethical?!”

“You and me both, kiddo,” Toshinori sighed. His knees cracked and the man groaned in pain as he lowered himself beside his protege. 

Izuku had studied marine biology at the famed Yuuei Academy of Sciences. In his final year, he was granted an internship at the Dagobah Wildlife Rehabilitation Center. Toshinori had always been a hero of his, but getting to work alongside him was like a dream come true. Three years post grad and he still had to pinch himself some days to make sure it was real.

“He spoke,” Izuku whispered, staring down at the mer’s relaxed face. “I’ve never heard them use our language before. But h-hearing him say it hurt…” Pain clenched around his heart and his throat tightened as he tried to hold back tears. “He can’t go back.”

“Most likely not,” Toshinori exhaled slowly. 

Izuku dragged his gaze over the magnificent creature’s body. Tanned skin faded to black scales that shimmer orange in the light that tried to shine through the thick clouds above. Thick, powerful. He was built for speed - probably could capsize a small vessel with the right angle. But that was before the mer had been caught by a propeller and then tangled in that awful net.

Toshinori patted his shoulder and wheezed as he stood again. “You should take care of that bite.”

A gloved hand rubbed under his nose, coming away slick with snot. Izuku scrunched his nose and sniffled. “I’m gonna stay with him. It’s not that bad, really. Got more of my wetsuit than anything.” The older man raised a brow, expression morphing into one of distrust. “Honest. I’m more worried about him.”

The boat lurched forward, engines rumbling loudly as they headed back toward shore. With a storm incoming, they rocked over the waves unevenly. The motion made Izuku’s stomach flip, but he refused to leave the mer out here alone, even if he was secure in the tarp. Toshinori’s steps faded as he entered into the lower decks.

Emerald eyes glared at the wounds inflicting the beautiful mer. Half his fluke was gone, lacerations carving up most of his scales to reveal the dark pink flesh beneath. Izuku swallowed back bile. It must have been awful. And even worse, all that thrashing he did in the net dislocated a few vertebrae. Izuku had snapped them back into place, but seeing the mer freeze and vomit through the action just made the biologist want to throw himself overboard. He was supposed to help these creatures. Sometimes that required a bit of discomfort, and he hated it. After a little over four years of rescue and research, this was the worst injury Izuku had ever seen. He tried not to think about it, but there was a chance the mer wouldn’t survive. Injury to the tail often proved fatal.

When the brightly colored buildings of the seaside town came into view, the adrenaline had fully run its course. It left Izuku feeling drained and overwhelmed. His throat tightened again, shoulders shaking as he held back everything he was feeling, but it was no use. The first sob led to a complete breakdown, voice going raw as he screamed out his frustrations at the thundering sky.

The sound of trickling water made Katsuki’s earfins flick curiously. The groggy heaviness of a prolonged sleep left him feeling numb and disoriented. His gills fluttered in the water and he coughed. The salt content was strange. It tasted weird on his tongue. A sharp, foreign substance. 

Scarlet eyes snapped open as his memories came rushing back. The humans! They had abducted him, carved him up to eat him whole. His tail throbbed painfully as he twisted in the shallow, rocky pool. Something synthetic was wrapped around his scales. He poked it cautiously and hissed when it stung. More gently, Katsuki grazed his webbed fingers over his limbs. Scrapes and scratches littered his skin. He could see angry, red lashes between the shimmering black of his armored scales. They radiated with heat and the itch of injury. 

Further down, where the wrappings were, throbbed with a deep ache. The mer’s stomach flipped and clenched as he remembered the overwhelming pain that surged through his body under the human’s hands. Prodding and squeezing softly, Katsuki froze as he got to the end of his tail. Pain flooded his body. His fins! His fins were gone!

A pained wail shook in the water around him as he tore at the bindings. Blood flooded the strange salty water, coating his tongue with a familiar taste of iron. Even through the haze, he could see the torture he’d been put through. Half his fluke was gone. Misery trilled in his throat and shook his earfins. His tail was broken! The human’s had hacked it off!

Metal squealed on rock and vibrations thundered above. Katsuki clawed his way to the surface. Bright lights burned his sensitive eyes. White walls surrounded him. His heart dropped into his stomach, face twisting into horror. They had captured him. The humans were going to take him apart piece by piece until there was nothing left.

“Shit. IZUKU!” The human on the platform above him yelled. Another flurry of vibrations and then the green one appeared. “He tore through the bindings.”

Katsuki saw red. That one. It was that one who took his tail. Katsuki was going to kill him. With a murderous screech, he launched himself out of the water. Pain surged up his spine and he wailed as his chest slammed against a wall. He couldn’t propel himself the way he could before they took what was his. The mer screeched again, swiping at the platform angrily. Emerald eyes set in a pale face stared down at him in panic. 

“Kill you!” The mer screamed. “I’ll kill you!”

The green one stared in horror, only backing away from the predator when the purple one grabbed hold of his arm and pulled hard. 

“Izuku,” the purple one hissed. “Get Toshinori.”

But those green eyes continued to stare into Katsuki’s furious ones. The mer continued to scream threats while swiping at the platform. His tail hurt so much with every attempt to launch himself out of the water, but Katsuki wouldn’t stop until the human’s throat was crushed between his jaws. 

“Go!” The purple one growled. It was only with a push that made the green one lose his balance that had him pulling his unblinking gaze away from the murderous creature.

Katsuki dropped back into the water, gills flapping wildly from the exertion. He roared in the water. Damn it! The beast got away! Aching and clenching his jaw, the mer swam back and forth, fists punching the wall each time it got in his way. Scarlet eyes tracked the purple human from below, muscles thrumming with aggression. Damn them! Damn all of them to the depths!

A sharp pain to his shoulder made Katsuki jolt. His vision went fuzzy just like on the boat. He was dragged to the bottom of the shallow, human made tide pool as his body stopped responding. Katsuki swore he’d kill them all.

“And where do you think you’re going?” 

Izuku froze, fingers gently curled around the door handle. With a wobbly smile, he turned to look at his superior. Aizawa held an expression of bored annoyance, arms crossed as he glared at the younger biologist.

“Um, I was just going to-”

“Yagi clearly told you not to go anywhere near our new patient,” the taller man sighed. “Your presence aggravated him into a frenzy. Not to mention the bite on your arm is still healing. We don’t want another repeat.”

“Yes, Sir.” Izuku deflated and turned to fully face him. He slipped a bag behind his back and Aizawa raised an eyebrow. “I I understand, but-”

“No buts, Midoriya. You have clear orders to stay away. If you’re so keen to advance your research, why don’t you spend some time in Denki’s enclosure.” The older man reached one hand out. “And give me the bag of fish.”

Izuku huffed in defeat and pulled the bag out from behind his back. It was snatched up harshly, making him jolt. The young marine biologist trudged back the way he came, heading for the other rehabilitation pools. 

The long hallways were unpleasant with their harsh fluorescent lights and gray concrete flooring. They didn’t even have pictures of the creatures they had rehabilitated over the years. Just a boring tunnel to get from Point A to Point B. 

Izuku huffed as he stuck his hands in his pockets. He really thought his plan would work. Sneak into the new mer’s enclosure and bribe him with snacks until he stopped trying to attack the human who saved him. 

A metal door scraped against the concrete at the end of the hall. Toshinori stood there, eyeing Izuku curiously. The young biologist avoided his gaze and ducked into the nearest enclosure. Humidity clashed into him like a wall, the sound of trickling waterfalls echoing in the space. Tropical plants with massive colorful blooms lined the rocky edge of the deep pool. The surface rippled and out popped a head of dark hair flattened by water saturation.

“Hi Momo,” Izuku smiled with a small wave.

The mermaid rose higher out of the water and waved back in a grand gesture. A smile parted her lips, showing off pointed upper and lower canines. They were different from the new mer who had a mouthful of serrated points that caused a lot of damage. That Izuku had experienced firsthand. The other difference was her coloring. Where the new mer was colored in onyx scales that were rough like armor, Momo was vibrantly colored. Bright red, iridescent scales covered the mer from hips to fins, rounded and soft. No bony sailfin, either. Instead, silky fins that looked delicate, but were actually quite durable fanned out from her scapula like a cape. She was magnificent in the water. Elegant and poised. 

Aizawa had saved her from a black market auction. Though she didn’t speak, she very clearly understood human speech and even many objects only someone who spent a lot of time on land would know. The team had deduced she was either taken captive as a guppy or born into captivity with the intention to sell her to rich assholes who collected exotic creatures. As such, Momo was never going to be returned to the wild. She seemed happy enough here, with her tropical home and sloping pool where she could choose to stay submerged or sunbathe on one of the rocky outcroppings that flanked the waterfall. There was even a viewing window on the lower level where visitors could observe her. She seemed to really enjoy when school groups came through.

A splash crashed against the rocks as the mermaid pulled herself up onto a rock. A chittering of noises caught Izuku’s attention. Momo’s mouth was moving in a flutter on mermish, teeth clicking and throat trilling as she pointed harshly at Izuku’s bandaged arm.

“Oh this?” The biologist pulled his hand out of his pocket. “Just a little bite.” 

The mermaid cooed softly and waved her hand, urging him closer. Izuku knew to be cautious around any mer, domesticated or not, they were still unpredictable at times. But he’d swam with her before and Momo had been nothing but gentle. When he was standing at the edge of the pool, cargo pants becoming damp from the humidity-covered plants, the mermaid snatched his hand and brought it close. 

“Nothing to worry about. Just a little itchy, but it’s almost healed.” Izuku chuckled as she pressed a kiss against the gauze. “We picked up a new mer three days ago. Just off the coast. His fluke was cut up by a propeller and he’s got a lot of lacerations to his tail.” 

Momo’s warm eyes stared up at him in worry. She trilled out a few noises that sounded like a question.

“Yes, I think he will be alright,” Izuku nodded. “It’ll take time and a lot of patience. He may even become a permanent resident like you.” His mind wandered to his last visit, hearing the mer screaming about killing him with so much fear and fury in his sharp eyes. “I-I don’t think he likes me much, though.”

Momo patted his hand gently and chirped.

“You’re right,” the biologist smiled. “He’ll come around eventually.” 

Izuku reclaimed his hand and took a few steps back. The mermaid flourished her tail, extending her silky fins to float atop the water in a mesmerizing display. Like most distinctions between male and female, she had breasts. Though unlike movies and television, they were covered in scales that extended up the side of her neck and over her cheekbones. They were softer than the scales on her tail and a bit more pink than red.  

“Toshinori doesn’t want me going anywhere near the new mer, but I really think if I just spend a bit of time with him, get him used to my presence, he won’t go into a frenzy like last time.” Izuku sighed and took a seat on the mossy ground nestled between a couple of plumeria blooms. “I don’t know what to do, Momo. I want to help. I mean, I was the one who got him untangled from the net and reset his dislocated joints. But maybe he just associates me with pain.” A freckled hand slid into his hair and gripped his curls tightly. “Oh, that would be awful!”

Momo chirped with a gentle nod. At least someone understood his plight. Too bad she couldn’t give him advice he could fully understand.

Suddenly, the mermaid sat up sharply and dove into the pool. Water splashed everywhere, drenching the edges of the enclosure, and Izuku along with it. The biologist sputtered and angled himself to peer into the water. It looked like there was a group standing at the viewing window. Izuku shook his head. He huffed a short laugh as he stood and wrung out the water from the hem of his shirt. 

“Kids show up and suddenly, I’m chopped liver,” he chuckled. “Oh well.” Emerald eyes peered around the enclosure. It was nice. Way nicer than the one their new resident was currently residing. “Maybe we can make his new home feel a bit more welcoming.” A plan was already forming in Izuku’s mind as he headed for the exit. Mumbles vibrated against his lips as he imagined the details, the materials, the vision. Now, how to put it all into action without getting reprimanded or eaten?

Almost two weeks in this shithole. Humans coming and going at strange hours, forcing him to conform to their schedules. Katsuki bared his teeth at the sound of the heavy metal door scraping open. The last time any of those tailless bastards came in here, they tossed stinking frozen fish into the water and jabbed him with sharp objects. Torturous beasts!

Scarlet eyes peered through the gentle distortion of the water’s surface. He couldn’t see anyone yet, but he could certainly feel the vibrations of their feet from above. Good. They were keeping their distance. 

The mer glided across the bottom of the pool, stomach just barely grazing the smooth ground. Pain still throbbed through his tail occasionally - phantom pains where his missing fluke used to be. The bleeding had stopped days ago, though there was still stiffness at the base of his tail that sent sharp jolts up his spine if he kicked too hard.

Katsuki hated this place. The water didn’t feel right. The saturation of salt was too little, making him feel heavy. The fish were cold, already dead. What was the point? He was a hunter! An apex predator! Damn humans treating him like a guppy. It pissed him off!

A crash from above accompanied by a shout had the mer halting. Earfins adjusted slightly as Katsuki tried to assess what the hell was going on up there. A distorted shadow of green appeared and the mer raced to the top. Water splashed over the metal platform above the tank as he broke the surface with a rumbling hiss. His sailfin was extended, reaching a height of one meter at the tallest spine. The vibrant orange hue segmented by sharp onyx spines was a warning.

“U-Ummm,” the green human stuttered and stumbled back. 

Katsuki’s eyes narrowed. He was back. The mer opened his mouth with a sharp click and hiss, showing off his jagged rows of serrated teeth. The human twitched and gazed at his arm. Scarlet eyes followed, making out a semi-circle scar that perfectly matched Katsuki’s jaw. The mer snorted. Served the bastard right!

“I-I’m just trying to make things more comfortable for you.” The human cleared his throat and waved nervously at the cart of foliage. A tree had fallen over. Probably what Katsuki had heard from below. “Sorry if I woke you. I was trying to be quiet. You’re crepuscular right? Active at dawn and dusk.”

Katsuki tilted his head. Shit. This one knew his hunting patterns. No wonder he’d gotten caught! The mer snapped his teeth threateningly and dove beneath the surface again. Large green eyes set in a tan face peered down into the water. It sent a shiver down Katsuki’s spine. 

He darted to the opposite corner, but upon looking up, knew the human could still see him. There was nowhere to hide! Katsuki’s heart pounded against his ribs, gills fluttering madly as he darted from corner to corner. No luck! His whimpered and flinched as pain shot across his nerves. Memories of agonizing cuts while hands held him down sent a spike of fear coursing through him. Trapped! Nowhere to hide! Pain! So much pain! Katsuki screeched and dove for the corner slightly obstructed by the metal platform. He coiled in upon himself tightly and covered his head with his webbed claws. 

“I can’t see him, he can’t see me,” Katsuki chanted to himself. He knew it was a lie, but there was absolutely nothing he could do unless the human came closer. Then, he could pay back that bastard for taking his fins and holding him captive. “I can’t see him, he can’t see me,” the mer whispered again. 

Memories flashed behind his tightly closed lids - the burn of adrenaline in his veins that forced him into fight or flight mode and straight into that damn net. The panic that overwhelmed him, forcing the wires deeper into his skin and scales. The wall of bubbles distorting the human who cut him out and dragged him onto that ship. Katsuki coiled tighter, ignoring the throbbing pain at the tapered end of his tail. 

He wasn’t sure how long he relived the worst day of his life, but the next thing Katsuki knew, the scent of fish reached his tongue. One scarlet eye peeked out from under flattened bangs and webbed claws. The mackerel floated toward the bottom in the center of the pool. About halfway down, it thrashed and darted through the water, overcoming its moment of being stunned. 

Predatory instincts kicked in. Katsuki held himself very still. Slowly, so slowly, he uncoiled his tail. His gaze never left the confused little fish. Gills opened and closed at a slower rate. The mer opened his mouth to taste the water, eyes rolling back in pleasure at the scent of fresh fish. None of that frozen, expired crap. This was the real deal. 

He shot forward, normal speed reduced by the loss of half his fluke and his command over direction a bit tricky. The predatory mer listed to the left, but readjusted with a growl and flourish of his webbed claws. Still, the mackerel had been too stupid and blind to realize what was happening. Serrated teeth gashed, cracking bones and swallowing the little fish down in two gulps. Katsuki hummed in satisfaction. It was divine.

A loud SMACK from above and then two more mackerel were floating down, down, down. Katsuki growled at the refracted image of the green human. He was stunning the fish and tossing them in. With a hiss, the mer darted toward the surface. A startled gasp shook his earfins and he reached out toward the sound. Webbed claws wrapped around something solid. Katsuki wrenched it into the water, attacking it violently. Bits of rubber tore off and floated in the water. He thought he’d dragged the human in, but he’d only managed to take a single boot. 

“Hey!” The human yelled from above. Loud enough for the word to be heard clearly underwater. 

Slowly, Katsuki ascended, only partially lifting his head above the surface. Water lapped at his nose. He exhaled harshly, nostrils flaring with a spray of salty droplets.

“I saved your life, you know!” The green human shouted, stomping his socked foot against the metal platform. It squelched, soggy with water. Spiny black earfins flicked in annoyance. “That’s right! If it wasn’t for me, you would have drowned in that net after getting your fins hacked off by a propeller!”

Propeller? Katsuki rumbled, bubbles permeating the water’s surface. There hadn’t been any boats. Just hulking metal monsters stacked with even more metal boxes. This human was the one who took his fins! 

With a harsh flick of his tail that made him flinch, Katsuki lifted himself out of the water to his shoulders. “Liar!” He pointed harshly, hand whipping water at the green human. “You take Katsuki fins! Give back!”

Emerald eyes blinked dumbly as the human’s mouth opened and closed like a fish. He swallowed harshly and Katsuki’s gaze followed the movement.

“You think…I-” Tanned hands flew into the nest of verdant curls and the human’s lips moved rapidly as words tumbled out of his mouth. “Of course! You were so distressed by getting caught in the net. And then I showed up, dragged you out and you were subjected to medical treatment that could be mistaken for torture. I had to set your broken vertebrae which must have been incredibly painful. Oh god! You must have thought I was hacking off your tail. I swear I was just trying to help.” He took a deep breath, turning to look at Katsuki as salty droplets slid over freckled cheeks. “You must have gotten hit by a boat which sent you into a defensive mode. If you were focusing on an unseen danger that explains how you got caught in the net. I was the one who saw the blood in the water first. Begged Toshinori to check it out even though he was convinced it was just a shark feeding frenzy. But then I saw you. You’re magnificent and it was…it was killing me to see you tangled and struggling. I had to help! I wasn’t going to let you die! JUST LET ME HELP YOU, PLEASE!” His chest was rising and falling rapidly, face screwed up as if he was in pain. “I just want to help you,” he whispered.

Katsuki sunk back into the water, just peering over the surface. This human was strange, and too loud. But there was something so raw and honest in those eyes that the mer was compelled to believe some of what he said. But he couldn’t trust him. Humans were liars. They polluted his home, stole his food, tortured creatures like himself. 

Suspicious scarlet stared back at earnest emerald. Katsuki’s gills opened, once, twice, three times before he broke contact and dove underwater again. A thump sounded from above and the mer spotted the human sitting on the metal platform, head covered by tan hands. 

He eyed the mackerel and licked his lips. Hmm, they could wait until he gathered his trash first. Webbed claws grabbed the torn up boot and its scattered pieces. He took his time rising to the surface, gently poking his head out to peer at the forlorn human looking stupid wearing only one shoe. 

Katsuki swam over and placed the torn up boot and its jagged bits on the platform. The human eyed him with curiosity, staying very still as the mer pushed it closer.

“Thank you,” he said, slowly pulling the broken shoe closer. Green eyes tracked the mer as he backed off and floated barely above the surface. Quiet tension shifted between them as the human poured water out of the boot. Just before Katsuki dipped under, he spoke. “Katsuki.”

The mer’s eyes widened, hearing his name spoken for the first time in a language not his own. It sounded strange without the usual trill from the back of the tongue. 

The human pointed at him. “Katsuki.” Then he flipped his hand to point at his own chest. “Izuku.”

Katsuki nodded once and dove to the bottom of the pool. “Izuku,” he muttered to himself. It sounded different underwater, almost as if it got caught in his throat. The mer growled and locked onto the dumb mackerel swimming nearby. Still, he couldn’t be too angry. The sight of trees and plants was already more comforting than the harsh brightness that had been there before. And no more frozen fish. Katsuki hissed at the surface of the water where Izuku finally stood and moved away. Damn that human!

A pencil scribbled fast across the page of a notebook. Izuku muttered under his breath about all the things he noticed in his encounter with Katsuki. Katsuki ! He had a name! The biologist drew a quick sketch of the mer’s impressive sailfin. That was twice he’d gotten a good look at it, from two different angles. The situations in which it flared gave Izuku the idea that it was used as an intimidation display. There was still a possibility the colors were vibrant to attract a mate, but there wasn’t evidence of that yet. 

“Crepuscular, serrated teeth, intimidation display,” Izuku muttered to himself. A ping chimed on his laptop and he looked up from his notes before doing a double take. “Shit.” 

Safety & Conduct Meeting 1:00pm

Conference Room 3, Floor 2

“That’s in 20 minutes!” Izuku hissed. His stomach dropped. “Oh no. Someone must have seen me either going into or out of Katsuki’s enclosure.” He gulped and stared at the meeting notification again. “I am in so much trouble.”

“I’d say.”

Izuku yelped and whipped around. A smirk pulled at Shinsou’s lips as he sipped on his usual lunch time iced tea.

“Stop sneaking up on me!” he hissed at the purple haired marine ecologist. 

“I don’t sneak up on you,” Shinsou snorted and took a seat at his desk. “You’re just too wrapped up in your notes to notice anything going on around you.”

“I pay attention,” Izuku defended.

“Not according to the security footage showing our newest resident trying to give you the Deep Blue Sea treatment.”

“It looked that bad?” The biologist cringed. 

“You’ll be lucky if the bosses don’t suspend you.” Shinsou eyed him for a long moment. “What were you thinking? He literally screamed that he wanted to kill you the first day he was here.”

“He’s scared, not a killer,” Izuku snorted and looked back at his notes. 

“That bleeding heart shit ain’t gonna cut it when Aizawa gets his hands on you.”

The biologist scrubbed his face and groaned. “I know,” he whined. With a deep breath, Izuku leaned back in his chair. “I know I can help him.”

“Your presence aggravates him.”

“He can speak full sentences.”

“No fucking way.” Shinsou snorted. “That’s just your imagination. Probably a fear induced hallucination.”

“Fine, don’t believe me,” Izuku sighed dramatically as he packed up his notes and tried to come up with a defense that wouldn’t lead to his immediate termination. “Guess, you’ll never know his name.”

Izuku had one foot out the door when Shinsou cleared his throat. The biologist threw a glance over his shoulder.

“Fine, I’ll bite,” the purple haired man said lightly.

Teeth dug into the freckled man’s lip. “Actually, I think I’ll keep that information to myself. Might help me keep my job.”

Shinsou rolled his eyes. “Good luck.”

The long walk to the lobby and elevator ride one floor up was just enough time for Izuku’s knees to begin shaking. He loved this job! Helping animals, furthering his research in all things mer, it was a dream come true! But he had gone against a direct order… twice . Things were not looking good. Even worse when he got to conference room 3 and saw not only Aizawa waiting for him, but also Toshinori. 

Izuku gulped. The last thing he wanted to do was disappoint his mentor. With a shaky breath, he knocked.

“Come in,” Aizawa’s voice ordered in a monotone.

Every nerve in Izuku’s body vibrated with potential energy. Adrenaline burned in his veins as fight or flight response kicked in. 

“Take a seat,” the dark haired man told him.

Izuku did as asked, sorting out his notes and papers so he could gather his thoughts without staring into two sets of intense eyes aimed at him. Toshinori cleared his throat and watery emerald eyes rose to meet his superiors’ faces.

“I’m sure you know why you’re here, Midoriya,” Aizawa sighed. “So, let’s just get down to the uncomfortable part.”

“W-Wait,” Toshinori stuttered through a cough. “Before we talk disciplinary action, I’d like to know why you disobeyed a direct order.”

It was so hard to look into those bright blue eyes. Izuku shuddered and sucked in a shaky breath. The tension in the room was suffocating. Trembling freckled fingers flipped open the beat up notebook. Not trusting himself to speak, Izuku slid it over to Toshinori.

The older biologist unfolded a set of reading glasses and picked up the notes. It gave Izuku some time to sort through his thoughts.

“I believe I’m the best person to oversee his care,” he said, voice tight. 

“And why is that?” Aizawa asked. At least he was humoring him instead of automatically dismissing the declaration.

Izuku opened his mouth to answer but was cut off by his mentor. “You got all this from just a single encounter?” The younger biologist nodded. “Katsuki…is that the name you decided to-”

“No. It’s what he calls himself,” Izuku shook his head. “He can speak in nearly full sentences. I don’t know how. Maybe he spent time near the docks and picked it up. The point is…” he swallowed, not sure if the next thing he said would help or hurt his case. “I know why Katsuki was so agitated when I was nearby.” He could see Aizawa about to shut down the whole conversation, clearly not believing a single word. “He thought I was the reason he’s missing part of his tail.”

“What?” Toshinori gasped. “That’s not possib-”

“I think his fight or flight response was activated when he was struck by the boat and since he wasn’t 100 percent focused on anything but getting away from danger, that’s how he got entangled in the net.”

“That’s just a theory, Midoriya,” Aizawa sighed. “This has always been your problem. You need facts. Stop making up stories about what could have happened. There’s no way for us to know exactly what caused his injuries.”

“But it’s the truth!” Izuku implored. “Please, I promise if you go down to his enclosure and call his name, he’ll respond.”

“He’s an aggressive predator who needs rest. I will not listen to this nonsense-”

“But he needs more than just rest and care. Katsuki has gone from an entire ocean to a pool the fraction of its size with limited mobility. But that doesn’t mean he’s helpless. I gave him live mackerel and he hunted just fine.”

“You better not have put that on the company card,” Toshinori sighed.

“I didn’t, I swear,” Izuku shook his head. “Paid out of my own pocket.” He turned back to Aizawa. “I’m sure the security footage looked bad, but I was never in any dan-”

“Not in any danger?!” The dark-haired man stood and slapped his hand on the table. “The only reason we’re not fishing your body out of that enclosure is because that mer only caught hold of your boot. Had you been even an inch closer-” he breathed heavily and swiped his other hand through his hair. “I don’t want to think about that outcome.” Normally tired eyes stared at Izuku with so much sharpness. “Safety rules and direct orders are meant to be followed for everyone’s benefit. They are not recommendations or loose guidelines. We have certain protocols in place to keep both the animals and our staff out of harm’s way.”

Izuku tried to protest.

“This is a direct order, Midoriya,” Aizawa leaned forward. “Do not, under any circumstances , go into that enclosure again.”

Tears pooled in Izuku’s eyes, blurring his vision. His lips trembled. He swallowed through the tightness in his throat. Emerald eyes squeezed shut, sending salty droplets dripping over freckled cheeks. He lowered his head in respect, “Yes, Sir.”

The sound of papers being gathered and a chair scraping across the floor echoed in the room. Izuku kept his breathing shallow, his shoulders hunched to make himself as small as possible. A heavy hand landed on the back of his neck, heating his skin.

“It’s for your own safety, kiddo,” Toshinori whispered. The large man was gone the next moment, following Aizawa out of the room. 

The door fell shut with a click.

“I just wanted to help,” Izuku sobbed. His shoulders shook violently as tears flowed over his cheeks. Shaking hands swiped at his eyes. His chest rose and fell rapidly in the beginning of hyperventilation. “I just wanted to help.”

A disturbance at the surface of the pool had Katsuki peeking one eye open. A distorted silhouette of a very large human appeared to be looming over the water. The mer backed into the corner. He didn’t recognize this one. 

Frozen fish sunk to the bottom. Lifeless and unappetizing. 

Katsuki grumbled and glared at the offensive offering. He wanted live mackerel. Or tuna. He slid his tongue carefully over the back of his sharp teeth. The mer kept his eyes toward the surface as he used his hands to crawl along the bottom of the pool. He snatched the frozen fish and darted to the surface. The big yellow human had turned his back. Perfect target. With a crank of his arm, Katsuki chucked the popsicle fish across the room.

“Gah!” The human startled when the icy offering hit him.

Katsuki dove back down and curled into the corner under the metal platform. He snickered at the dumb look on the big human’s face as he peered into the water. 

“Katsuki!” A deep voice called, and fear shot through the mer. 

Shit! He knew he’d slipped up horribly when he told the green one his name. The big human called again. Cautiously, the mer rose to the surface, keeping his distance.

“Hello,” the yellow man bared his teeth in a smile. Katsuki showed off his serrated ones in warning. “You really are gorgeous. It’s no wonder Izuku is so taken with you.”

Earfins twitched at the familiar name.

“So, he was right. You understand human speech.” The man groaned, joints popping as he took a seat on the concrete ledge leading to the metal platform. “Izuku also says you can speak.” He held out a frozen fish.

Scarlet eyes glared at it. Katsuki scoffed and snapped his teeth.

“Hmmm, you don’t like these very much, huh?”

The mer snorted and dipped beneath the surface, reappearing closer to the platform. “Deku.”

“What’s that?” The human asked.

Katsuki pointed at the nasty popsicle fish. “Deku bring mackerel.”

“Oh oh I see,” the yellow man nodded. “Izuku brought you live fish.” 

He produced a clear bucket filled with mackerel swimming in circles. The mer licked his lips and inched forward, hunger trumping caution.

“Tell you what,” the man said. “We’re going to have a conversation to get to know each other. For every question you answer, I’ll give you one of these.”

Scarlet eyes tracked the hand that dipped into the bucket and snatched a wriggling fish. 

“My name is Toshinori,” the man stated. “What should I call you?”

“Already know name,” Katsuki sniffed and held his hand out expectantly. When Toshinori didn’t immediately pass over what he wanted, the mer snapped and slapped the water angrily. “Katsuki answer, now Toshi-no-nori give fish.”

The mackerel plopped into the water next to him and Katsuki dove to snatch it between his sharp teeth. He was still crunching through bones, blood and scales stuck to his chin when he returned to the surface. Toshinori’s expression had changed. His eyebrows were nearly touching the soft strands of yellow and his lips were parted in awe. The man grabbed a radio.

“Toshinori to Aizawa,” he called. Katsuki eyed the bucket of fish as he licked the remaining blood from his lips. “You’d better get down to Katsuki’s enclosure.”

“ We are not seriously calling him that. Midoriya always gets to you. ” A pause. “ Fine, I’m on my way .”

“Who talk?” Katsuki asked, looking around the room. “Where hiding?”

“It’s a radio,” Toshinori explained. “So we can talk over long distances. Kind of like a whale song.” Fingers tapped at his knee. “My friend is on his way.”

“Deku?”

“No, not Izuku. Aizawa.” The human responded. “He has some questions for you, too.”

“Katsuki get fish if answer?” The mer asked.

“Yes, exactly.” Toshinori nodded. “How did you learn human speech?”

“Many human near home. Loud, dirty.” Katsuki reached his hand out for another fish when the door scraped open. 

Caution overrode the reward and the mer dove back to the bottom of the pool. Muffled voices drifted to the depths and a new shadow appeared. It was dark, scary. Katsuki didn’t like this. Too many humans, nowhere to hide. 

“Katsuki!” Toshinori called. “It’s okay! This is Aizawa!”

The mer took a deep gulp and willed his heart to slow from its rapid pulse. He approached the surface again, this time only peeking his eyes out of the water. The human standing beside Toshinori was not as tall, but no less intimidating. It seemed a bit ridiculous that a mer his size could be so nervous, but Katsuki had seen what these monsters were capable of. He couldn’t trust them so easily.

“Hello Katsuki,” the man in black said in a gravely tone. 

“You can ask your questions,” Toshinori said. “I promised him mackerel if he answers.”

“I’m Aizawa,” he said, crouching down with much more ease than the yellow human. “Can you tell me what happened to your tail?”

Scarlet eyes blinked at the pair of humans, bubbles rising to the surface from the mer’s nostrils. “Human take,” Katsuki said, finally lifting his head out of the water.

“How?” Aizawa asked. The mer pointed harshly at the bucket of fish. The man rolled his eyes and threw a mackerel into the water. “Now answer this one. How did humans take your fins?”

Between crunches, Katsuki spoke. “Katsuki think Deku take, but Deku say boat.”

“Who the hell is Deku?” Aizawa hissed up at Toshinori. 

The yellow human tossed a fish in the water. “That’s what he calls Izuku.”

“Your protege gives me a headache even when he’s not here,” the black-haired man scoffed. He turned back to Katsuki with a sigh. “Izuku is correct. We think you were sliced by a propeller. You’re very lucky you didn’t die.”

The mer blinked. “Katsuki go home?”

Toshinori placed a large hand over his mouth and rubbed his chin. Aizawa wouldn’t look at him. 

“Katsuki go home!” The mer demanded with a snap of his teeth. “Katsuki go home!” He slammed his clawed fists against the water causing a massive splash.

“I’m sorry, Katsuki,” Toshinori sighed. “Because of the injury you sustained, we don’t think you’ll survive in the ocean.”

Katsuki felt all the blood drain from his face. His stomach dropped and he nearly choked as he forgot if he should breathe through his gills or nose. No! No no no no no! It couldn’t be true. But as wild scarlet eyes darted between cerulean and onyx, he found his answer. Katsuki screeched, vocal cords grinding unnaturally in his native tongue while above water. Both humans slapped their hands over their ears, faces scrunched in pain. 

The mer darted back to the semi-obscured corner of his pool and wailed. They were keeping him here… forever . He couldn’t - wouldn’t - let them! Katsuki could already feel his throat going raw from the song thrumming through him. Webbed claws slid down his tail to grasp his broken tail. Only half a fluke and deep pink scarring where chunks of scales were missing. The mer wailed again, mourning his loss of freedom. To never see the ocean again…it would be agony.

It was so hard to ignore that little voice in the back of his head, but Izuku did his best. Ever since Aizawa forbade him from ever seeing Katsuki again, the biologist spent more time with the other mers. Momo picked up on his sudden mood immediately, offering comfort in her own way. Denki didn’t seem to realize anything was off. But that may have had more to do with the fact that Shinsou was around.

Even though the ecologist didn’t spend much time interacting with the mers, one of them had taken a liking to him. Denki had been saved from an oil spill in the South Pacific two years prior. After almost 8 months of rehabilitation, the crew prepared to release him back into the ocean. It had been a big production with a news helicopter and everything. Except it didn’t exactly work out the way they’d planned. 

Denki refused to leave, chirping in confusion as the humans urged him to go home. When they turned back toward land, the gold and black striped mer followed them. It was Shinsou who spotted his scales under the bright spotlight of the boat and informed them of the situation. After a round of laughter, the team hauled the serpentine mer back to the wildlife rehabilitation center where he took up permanent residence. 

“You look like shit,” Shinsou snorted and kicked Izuku’s boot. 

“Yeah, well,” Izuku deflated. He didn’t have the energy for a comeback. “I feel like it, too.”

“Wow, Aizawa must have really put the hammer down if Sassdoriya doesn’t have anything to say.”

“I’ve never seen him so mad,” the biologist breathed and set aside his notebook and pencil. “No matter what I said, he shot me down. I thought for a second that maybe Toshinori would have my back.”

“He could have killed you,” Shinsou said seriously.

Tired emerald eyes shifted to look at his friend. “He had every chance to even after he ripped my boot to shreds…but he didn’t.” Izuku inhaled through his nose and let it out all at once, letting his lips flap loudly. “Just sucks, you know? It really felt like I was making progress. Katsuki understands human speech and he can even speak it very well.”

“He’s not like Momo or Denki, though, is he?”

Izuku shook his head and hummed. “No. He doesn’t want to be here. Which is why it’s going to be so devastating when he finds out he can’t go home.”

Shinsou sucked in a sharp breath between his teeth. Denki darted over at the sound but the ecologist waved him off. Such a protective mer. “I heard from Koda that Aizawa and Toshinori already broke the news…and he didn’t take it very well.”

“Shit. Is he okay?” Izuku swallowed. 

“You didn’t hear it from me, but I heard Toshinori on the phone this morning,” Shinsou said quietly, eyes shifting to the security camera in the corner of the enclosure. “I heard him say Dave.”

Izuku jolted and whipped his head around. “Dave? As in David Shield renowned Mer Expert?”

“Seemed that way.”

“Well, what else did you hear?” The freckled biologist implored.

“That Katsuki isn’t eating. Not even live fish. And that he hasn’t moved from the same spot in over 24 hours.”

Izuku jumped to his feet and snatched up his notebook. 

“Where are you going?” Shinsou drawled. 

“I don’t care if I get fired,” he snapped. “I’m not letting Katsuki die of depression in a too small rehabilitation tank.”

“No, don’t go,” his friend rolled his eyes in mock protest.

Izuku smirked at his friend’s support and darted out of the enclosure. His lungs burned with how fast and hard he was breathing, practically jogging down the hall toward Katsuki’s door. Green eyes shifted back and forth, looking for anything that might stop him from entering. Aizawa was probably still stuck in that board meeting that started two hours ago. And if Toshinori was worried about Katsuki, he was most likely holed up in his office researching methods to alleviate the situation.

The freckled biologist grabbed the doorhandle and paused. What was he even going to do? How could he fix this? He thumped his head on the door once. With a grunt, Izuku pushed his way inside. The trees, rocks and mossy plants he’d added to the enclosure made it less sterile and intimidating, but even he knew it wasn’t enough. 

“Katsuki!” he shouted. Izuku stepped down onto the metal platform and leaned over to peer into the pool. Curled up just below him was the giant black mer. How such a big creature could wrap himself into such a tight coil, he didn’t know. “Katsuki!” 

The mer didn’t even flinch. 

Izuku’s heart pounded in his throat. Adrenaline had kicked in and now, the biologist was certain the only way to help Katsuki was to do something very very stupid. He marched over to the access door next to the one that led to the hallway. Inside were various sizes of wetsuits and scuba gear. Already pulling off his shirt, Izuku stepped fully into the double wide closet and changed into one. 

With a groan, he shouldered an oxygen tank and grabbed a set of goggles. His hands shook as he tried to clasp the straps across his chest. Izuku was certain someone would see him on the security camera by now. His mouth had gone dry knowing these could be his last moments as a marine biologist…and alive on earth. 

His feet were bullied into flippers. With an awkward waddle, Izuku stepped down onto the metal platform once again. One hand pushed back his unruly curls while the other pulled the goggles over his eyes.

The heavy metal door scraped against the concrete with a bang.

“Midoriya, don’t you dare!” Aizawa shouted. His dark eyes were wild with fear as he watched Izuku pop the breather into his mouth and fall backward into the tank. “IZUKU!”

Water rushed in Izuku’s ears. Bubbles rose up around him, obscuring his vision slightly. He could hear and see how fast he was breathing through the scuba apparatus. He closed his eyes for three beats and calmed his anxiety. There was a job to do.

The biologist turned to face the bottom of the pool and was relieved to see Katsuki had taken notice of him. At least it was a reaction. Carefully, Izuku descended, feeling a bit of pressure the deeper he went.

“Kat-Kacchan,” Izuku called, unable to produce an ‘s’ sound with the breather in his mouth. Scarlet eyes tracked his movements and the biologist felt a shiver crawl down his spine. He was in Katsuki’s territory now.

That massive tail uncoiled, black scales flashing orange under the rays of fluorescent light that filtered to the bottom of the tank. Izuku knew his heart was pounding so hard there was no way Katsuki couldn’t feel the vibrations. A twitch of his earfins confirmed the mer was aware of his nervousness.

Izuku kicked with the flippers to gain a bit of distance. Being just under 173 centimeters tall, the biologist was relatively average in his height. But now, he was dwarfed in the water by an apex predator more than three times his size. He felt very small.

Scarlet eyes watched him carefully. An adjustment of the spiny orange fins that decorated his hips, a flash of spikes behind his back. Izuku swallowed hard. Katsuki was preparing to attack. One thing the biologist had learned from his years of research was that mer were very much like sharks. Never turn your back on them and no sudden movements that could be mistaken for distress.

“Kacchan,” Izuku tried again. “I know you’re mad.” 

The mer flashed his serrated teeth, lips pulling back to show off bright pink gums.

“But you have to know that returning to the wild would be very difficult.”

“Go home!” Katsuki rumbled with a snap of his teeth.

“You can’t.” Izuku snapped back. He knew it was a bad idea to rile up the distressed mer further, but there was no easy way to tell a captive animal they could never go home.”There are other mer here. You’re not alone.”

“Katsuki hunt alone!”

“You will die if you go back!” Izuku implored.

“Deku lies!” The mer screeched, fins shuddering with fury.

“I don’t lie, Kacchan! I would never lie to you!”

But it was no use. Katsuki darted forward. The resistance of the water made it nearly impossible for Izuku to defend himself quickly. The biologist yelped as his mask was jammed into his face. His nose throbbed, but that was the least of his worries. As Izuku blinked back tears of pain, he recognized the familiar hue of his own blood floating in the water. 

The breather was knocked out of his mouth and the next moment, his arms were bound to his sides. Black scales scraped against his wetsuit as the mer coiled around him tighter and tighter. Izuku’s lungs throbbed painfully and he heard the desperate gulping sound echo in his ears. Thrashing was no use. Katsuki’s hold was too strong. 

In one last attempt to escape, Izuku kicked down as hard as he could. Katsuki wailed in pain as the flipper connected with his healing wounds. The mer released his hold at the same time Izuku let all the air out of his lungs. Reaching for the breather, the biologist found that it had been ripped from the oxygen tank. He kicked hard to the surface, well aware that he’d just pissed off the predator even more. Fingers reached for the surface. Izuku was still too far down. On automatic, he sucked in water. It was agony as his lungs filled with liquid instead of air. 

A webbed claw wrapped around his ankle and Izuku felt his entire body revolt against him. The more he tried to kick, the more lackadaisical he became. His mind went fuzzy, both sending alarming signals that he needed oxygen and old, wistful memories of his time swimming in the ocean as a child. Onyx filled his vision as Katsuki came back into view. He watched as two small bubbles rose to the surface. Izuku’s body stilled, allowing the water to drag him however it saw fit. Those scarlet eyes bore into his unfocused ones, bright and fiery.

The sun hung high above his head as waves lapped at the shore. Details became clear the more Izuku looked around. The beach where he’d seen his first mermaid. Black sand separated between his wiggling toes. A blowhole in the rocks exploded loudly as high tide rolled in. And There, just a little ways past the dropoff where aqua waters darkened to navy, emerald eyes caught sight of opalescent scales. Only for a moment and then they were gone. A few seconds later a scalloped fluke appeared. 

Izuku felt water rush over him as he dove into the waves to follow. The snorkel sealed between his lips whistled loudly with each breath, excitement taking over. And then, shining white flashed just out of the peripheral of his goggles. A bright shout echoed in the snorkel and he turned to follow. Pale hair as silvery and ethereal as the moon floated below Izuku. He stayed as still as possible while treading water to not scare the beautiful creature away. Ruby eyes peered up at him from a pale face. Something about them sent a thrill down his spine. She looked young, face and skin not marred by years of hunting or territory battles. Pristine opalescent scales resembling the interior of an oyster caught the rays of sun beating against the ocean’s surface. 

In his eagerness to get a closer look, Izuku didn’t realize he’d dived under the waves. When he sucked in a breath, nothing happened. A jolt of panic shot through his system as he sucked again and saltwater filled his lungs. He kicked to the surface, effectively scaring away the young mer and coughed until he could take a breath without feeling the gargle of water in his throat. 

The scene changed suddenly. Dark clouds rumble above the rough waves. Izuku’s muscles screamed for a reprieve as treading water became a task of survival. Swells crashed over him, pounding him beneath the surface. Lungfuls of water flooded from his mouth, heated by his internal temperature. Distant voices screamed around him and Izuku knew there had been a disaster. And then everything stopped.

Emerald eyes cracked open, blinking rapidly against the bright light shining down on him. Pressure against his chest lessened but left behind a throbbing ache. The pain was exacerbated with each breath. Faces, distorted by confusion and the burn of saltwater, started to become clear. Bright blue eyes framed by canary blonde locks blocked the bright lights. The harsh drip drip of hot droplets slapped against Izuku’s pale cheeks. He groaned and everything rushed in. Lights brightened, voices clashed in a cacophony of shouts, the loud squeak of wheels on concrete. It was too much.

“Thank God,” Toshinori sobbed. Warm hands tucked under Izuku’s shoulders to lift him into a hug. 

Everything felt heavy, nerves tingling across his skin. His head hung back and Izuku wheezed. 

“Don’t move him too much,” an unfamiliar voice ordered. “We’re going to take him to Musutafu General to get him properly looked at.” 

Two sets of hands lifted Izuku off the hard concrete and onto a plush stretcher. An oxygen mask was fitted over his mouth and throbbing, swollen nose. Emerald eyes recognized the plain white walls and scarce foliage. He willed his neck to shift his head toward the tank he knew was on the right. Scarlet eyes watched the flurry of activity with a mixture of curiosity and caution. Katsuki clicked his teeth in combination with a low croon as the paramedics wheeled Izuku out of the enclosure.

“H-How?” Izuku croaked, voice raw.

“You fell into the tank and nearly drowned.” 

Dark brows pinched together. No, that wasn’t right. He’d jumped into the water on purpose, willingly put himself in danger to…to what? Katsuki had attacked him. There was no doubt that would be the outcome and now, as oxygen was pumped into Izuku’s lungs, he wondered what the hell he ever thought he’d accomplish. Like an absolute moron, he willingly put himself into an apex predator’s territory. A predator who had a history of being agitated by Izuku’s presence. Of course he’d be pissed…even more so since Katsuki had been told there was no way he would ever return to the ocean. 

“Who…pulled me…out?” Izuku wheezed through the question with effort. 

“Don’t know,” one of the paramedics responded. “You were already out and CPR was being administered when we arrived.”

Izuku pondered the unlikeliness of his survival the entire way to the hospital.

The humans were noisy above the tank. Katsuki peeked one eye open and growled at the surface. Didn’t those morons know he was trying to sleep? Deku knew. The green human knew a lot of things about him…his hunting patterns, that he preferred live fish to frozen, the types of plants that surrounded the rocky areas he frequented in the wild. 

Katsuki clicked his teeth and shut his eyes again, fighting the shiver that crawled down his spine as images flashed behind his eyelids of Deku floating lifeless in the water. He thought he wanted the human gone, but seeing him unresponsive sent fear rushing through his system. It wasn’t Deku’s fault he was trapped here. Katsuki knew that now. It was his own unobservance that caused him to lose half his fluke. Well, that an that fucking metal monster that struck him in the first place. 

Toshinori showed him a moving picture from the little box he called a phone. It was strange to see the ocean from the boat deck, but when Deku appeared shouting that they had to approach the bloody patch of water, Katsuki felt his heart clench. The green human was so adamant, a hardness in those emerald eyes as he shouted and pointed harshly. Then, Katsuki got to see Deku jump into the water and a few minutes later, his own wailing self being pulled onto the boat. The wounds were severe, like the kind Katsuki had witnessed on dolphins struck by human contraptions. The video ended with Deku sitting next to Katsuki, never leaving his side while all the other humans abandoned him. 

Whirring and scraping with the occasional thump or crash had the mer covering his earfins in annoyance. What the hell were they doing up there?!

He found out two days later when a blue sling invaded his tank. It reminded him of the one Deku had helped him into after cutting him out of the wiry net. Katsuki was cautious, circling the object but never getting too close. For hours, it sat just below the surface of the water. 

When the scraping and thumping stopped, the mer investigated the sling a bit more closely, touching it and jolting back when it swayed. He smelled it, finding nothing unusual other than the material it was made of. Carefully, Katsuki crawled into the center, feeling the sides and lying on his belly. It was more comfortable than the hard bottom of the enclosure. But then it moved and he was being lifted out of the water. With a thrash and a screech, the mer watched his angle change.

“You’re alright, Katsuki,” a stranger with a soft voice cooed. “I want to check to make sure your tail is healing. I know your…fight with Izuku got a little intense.”

“Deku here?” Katsuki asked, scarlet eyes darting around the now bare room.

“No, sorry. He’s at home. But don’t worry, he’s just resting now. No long-term damage from what I’m told. I won’t do anything to hurt you.” For some reason, Katsuki wasn’t as nervous around this human. He was calm, soft. “I’m Dr. Koda. I take care of all the animals here at the rehabilitation refuge.”

“Animals?” Katsuki asked before squawking as the sling started to move. The machine it was attached to carried him out the door and the mer perked up, curious to see what was beyond the four walls he’d been seeing for some time. More doors and a long tunnel appeared and he slumped. It wasn’t exciting at all! “Deku say other mer here.”

Dr. Koda nodded with a hum. “That’s right. Momo and Denki are permanent residents. The team has taken care of and studied many mer over the years, most of which were released back into the wild.”

“Katsuki released, too?” He asked hopefully.

The doctor rubbed the back of his neck. “Probably not. I’m sorry. The damage to your tail is too great. But I promise, we’ll do our best to make this a comfortable home.”

The mer deflated with a huff. It was worth a shot. Everyone had been telling him he was broken, enough that he was even believing it himself. In the wild, he wouldn’t have hesitated to kill Deku, but here… 

After only a month, Katsuki found himself being less cautious of certain humans. Toshinori was especially nice and understanding. And he didn’t mind Aizawa too much. Then there was Deku…who Katsuki had been feeling guilty about nearly drowning. In a moment of panic, the mer had grasped the lifeless green human and sealed their lips together. With a little effort, he was able to pull most of the water out of Izuku’s lungs and place him on the metal platform so the other humans could take care of him. He could admit, it was scary seeing Aizawa and Toshinori frantically beating Deku’s chest until he coughed up the rest of the water. A mixture of confusion and relief had flooded Katsuki’s body upon seeing Deku’s chest rise and fall, but still the human didn’t respond or even flinch when those strangers rushed into the enclosure. 

“Here we are,” Koda smiled as he opened the door to a scary looking room. Metal instruments, bright lights, unfamiliar statues. “Nothing here will hurt you.”

Katsuki wasn’t sure he believed him. Still, he had no choice. The sling lowered the bottom half of his tail and fins on a cold metal table. He flinched at the stark change in temperature. 

The doctor snapped some white gloves on and Katsuki’s eyes followed every movement he made there after. The mer flinched away when Koda tried to rub something sticky and wet over his scales, but he explained it was just gel for the tool he was going to use. A strange wand was pressed to his fins and a black and white picture lit up a screen. Katsuki gasped at the strange feeling of the wand and gel, wiggling to get away from it.

“Please stay still,” Koda said. “I can’t see properly if I can’t get a good look.”

The mer complied and only a couple minutes later, his scales were carefully wiped clean. 

“There’s inflammation around the two vertebrae Izuku set during triage and I’m assuming that’s where he kicked you when the two of you were fighting in the water,” the doctor said. “Does it hurt now?”

Katsuki nodded. “Better in water. Heavy on land, pull tail.”

“Right, of course,” Koda nodded. He shuffled around the room and pulled a few things from cabinets. 

The moment Katsuki saw a sharp needle in the doctor’s hands, he thrashed to get away. He hissed at the throbbing stiffness in his tail.

“Just a pinch, I promise.” And then he stabbed between dark, jagged scales. The mer tensed up, squeezing his eyes shut tight against the agonizing pain…but it never came. “All done.”

Slowly, Katsuki opened one eye and found the weapon to be gone. He blinked and relaxed.

“It’ll help with the pain,” Koda smiled and patted his tail gently. “I think you’re ready to move into your new home.”

The mer perked up at that, curiosity taking over as the sling swayed down the long tunnel once more. Scarlet eyes observed everything from tinted windows to humans shuffling between rooms. The doctor led toward the end before opening another heavy door. 

Awe widened Katsuki’s eyes as he took in the algae and moss-covered rocks and abundant waxy leaved plants surrounding a tank nearly three times the size of the one he’d been in previously. The mer whistled and trilled in excited curiosity. 

“Do you like it, Kacchan?” 

Blond spikes ruffled as the mer whipped his head around. “Deku!” 

The freckled human tangled his fingers in his verdant curls and smiled. “I’ve been working on this since we brought you here. And while I know it’s not the kind of home you were hoping for, I hope that this is a little more familiar.”

“Shouldn’t you still be at home, Midoriya?” Koda asked with concern.

“I’m fine,” Izuku responded. “Can we lower him in?”

“Of course,” the doctor nodded. “Ready Katsuki?”

The mer craned his neck, trying to get a better look at the pool. As the sling brought him closer, he noticed the ripples on the water’s surface. Anticipation burned in his veins and with a little scootch, Katsuki dove into the water. The salt content still wasn’t quite right, but it was far better than before. And just as he thought, those ripples at the surface were caused by currents. With tiny bubbles kissing his skin and the force of the water pushing his hair away from his forehead, Katsuki swam against it. His eyes closed and a smile stretched across his lips. It felt good. 

Interested in exploring more, he dove deeper to find a rocky cave. The mer peeked inside. Just big enough to hide away from prying eyes and pillowed with soft sand. Tiny lights twinkled from the ceiling. Katsuki laid on his back and looked up in wonder. It was like watching the night sky with its vast sea of stars. Giddy happiness made his stomach flip. He rushed to the surface, startling the doctor and making Deku flinch.

“Kacchan?” 

The mer waved him over, but the freckled human eyed him cautiously. His feet moved slowly and once he was on the other side of the line of waxy plants, Izuku crouched.

“Deku come,” Katsuki waved him closer.

Izuku scuffled closer, but he still was out of arm’s reach. The mer snapped his teeth in irritation.

“Can you answer one question first?” The biologist asked.

“Get fish?” 

A chuckle bubbled past Izuku’s lips. “I’ll bring some later. First, can you tell me why you saved me after trying to drown me?”

Scarlet eyes widened slightly and it seemed Izuku could see the surprise on his face.

“I know it was you,” he said. “Toshinori told me when he picked me up from the hospital. So…what changed your mind?”

Katsuki shrugged and averted his eyes. It was hard to look at the human, knowing things could have gone differently had he not had a change of heart. It wasn’t a singular thing that made the decision for him. 

“Deku save Katsuki,” the mer mumbled. “Deku not bad, Deku help. So, Katsuki save Deku.”

Those wide green eyes observed him for what felt like eternity. They sparkled with something Katsuki couldn’t quite piece together. Izuku blinked and a smile softened his features. Finally, he shuffled closer.

“Midoriya, please be careful!” Koda called.

The toes of rubber boots touched the edge of the rocks and Katsuki pulled himself out of the water so he was eye to eye with brilliant emerald. Izuku’s breathing stuttered, chest pausing as he went stock still. Slowly, the mer tilted his face and pressed his lips to a warm, freckled cheek. Then, he lowered himself back into the water and dove below the surface, leaving Izuku to stare after him in confusion.

“He seems to be taking well to the new enclosure,” Aizawa commented. One arm was crossed over his chest as he sipped from a steaming mug of coffee. 

“Kacchan likes the cave the most, but I’ve caught him smiling while swimming against the artificial current more than once,” Izuku chuckled. 

The viewing room colored them in soft blue light as they observed all three mer in the theater. Their enclosures weren’t connected and probably never would be since they all required different temperatures and salt content. But the windows between tanks allowed all three mer to see each other. Denki had been most curious about Katsuki, swimming back and forth against the window for hours until the giant black mer approached. Of course, it was only to pound the glass and gnash his teeth threateningly, but Izuku was sure the moody mer would come around to his neighbors. 

Momo waved as she passed by the glass, gliding elegantly through the water so her cape-like fins danced like silk. Katsuki seemed interested in her, watching the mermaid twirl and spin as she performed a graceful dance for their visitors. 

That was the other thing Katsuki hadn’t quite gotten used to. The school groups. Dozens of eyes watching in wonder at the size of him, pointing out his damaged tail. The great black mer often hid in his cave when children passed through, only coming out when Izuku tapped a particular rhythm on the glass. 

The biologist did so now and a head of blonde spikes popped out from the rocky cavern. Izuku grinned and waved. With a roll of scarlet eyes, Katsuki dragged himself out of his hiding spot and approached the window, gliding through the sea of kelp that rose from the floor. 

“I’m going up!” Izuku pointed toward the ceiling. The mer nodded and ascended. From his angle below, Izuku spotted the disturbance at the surface where Katsuki exited the pool in favor of the moss-covered rock bed.

“Please don’t do anything that’s going to get the board breathing down my neck,” Aizawa droned.

“Of course not,” Izuku grinned. His boss raised an eyebrow, clearly not believing him. 

The biologist cleared his throat and rushed out of the room to get to Kacchan’s enclosure. He’d been working on another project since he was hired on full-time at the wildlife center. It had taken a lot of hearings with the board to get approved, but now it was ready to go. The rehabilitation and research center connected to the exhibits of the aquarium on the other side. It had worked out that Kacchan was a local mer, allowing them to easily connect his new enclosure with the exhibit showing off dozens of species of creatures that also called the Sea of Japan home. And today, Izuku and Toshinori would be opening the door between the exhibit and Kacchan’s tank.

Nerves made the biologist’s hands sweat. There was reason to be worried. The great black mer was the most unpredictable of their residents. Case in point, Katsuki had kissed Izuku two weeks ago when he was introduced to his new home. Just five days prior to that, the apex predator nearly drowned him before changing his mind and saving him. 

“Deku!” Katsuki snapped the moment the door to the enclosure was opened.

“Hi Kacchan. How are you today?”

“No! No happy voice. Wake Katsuki from nap.” The mer pouted and crossed his arms.

“Well, it was for good reason,” Izuku rolled his eyes at the dramatics of the temperamental mer. Scarlet eyes shifted to him with curiosity. “Toshinori and I have a surprise for you.”

“Katsuki see no fish.”

“Always thinking with your stomach,” the biologist chuckled. “You see that door above your cave?”

“One with many fish?”

“Yes, that one.” Izuku nodded. “We’re opening it so you can swim between here and the exhibit.”

Katsuki licked his lips and patted his stomach.

“Hey hey, no! This is not so you can eat your fill!” Izuku protested. The mer deflated with another pout.

“There’s more space for you to move about and explore.” Toshinori explained as he entered. “There are humans, too. So, we’ll leave the door open in case you want to go back to your cave.”

The mer’s earfins flicked in interest. “Like ocean?”

“A lot smaller than the ocean, I’m afraid,” Toshinori sighed. “But big enough to claim as your territory.”

“No Dunce Face, no Fancy Fish. Only Katsuki,” the mer nodded.

Toshinori’s jaw dropped as Izuku snickered behind his hand. “Who is he-”

“Denki and Momo,” Izuku laughed. “Kacchan, those aren’t very nice names.” The mer smirked and shrugged. “But yes, neither Momo nor Denki will be there. They are from other parts of the ocean and wouldn’t do as well in your environment.”

“Ready to give it a try?” Toshinori grinned with a thumbs up.

“Give go,” the big mer nodded and slipped back into the water. 

“I’ll suit up,” Izuku announced.

“You’re sure about this?” Toshinori asked, grabbing his bicep. His grip was tight, fingers shaking with concern.

“I’ll be fine,” he nodded and patted his mentor’s hand reassuringly. “We’ve come to an understanding. Kacchan won’t hurt me again.”

Bright blue eyes shifted between his emerald ones. Finally, he released Izuku with a long exhale. 

“You know what to do if things go sideways,” Tishinori nodded. “Be careful.”

“Always,” Izuku smiled, knowing his words meant nothing. He was frequently the most impulsive of their little team. 

Katsuki peeked out of the water with a grimace. The young biologist heard the mer shout at Toshinori asking what was taking so long. The closet door swung closed and Izuku changed quickly. His heart rate accelerated to the pound his entire body vibrated with every thump. This was necessary. If he didn’t get back in the water now, there was a chance that fear of drowning would snowball out of control. And the last thing he wanted was to quit being a marine biologist because he developed a fear of water. 

“Get your head in the game!” Izuku hissed to himself and slapped his cheeks. The sting was needed to force him out of a spiraling headspace. 

With flippers attached and oxygen tank checked for appropriate levels, he waddled out of the closet. Scarlet eyes widened in surprise, an angry shout dying on Katsuki’s lips. The mer floated over as Izuku approached the edge of the water. 

“What Deku doing?”

“Coming with you,” Izuku smiled. “I figured, if you had someone familiar accompanying you that maybe it won’t be so overwhelming.”

“Deku not scared?” 

“A little,” the biologist admitted with a soft laugh.

“Katsuki protect,” the mer nodded sharply and reached his webbed hand out of the water. Izuku felt his heart flutter between his ribs.

He pulled his goggles down and took a deep, calming breath, exhaling slowly. With the breather popped in his mouth, Izuku grasped Katsuki’s hand and dropped into the tank. Water rumbled in his ears as an explosion of bubbles erupted around them.

Even as they approached the perforated plexiglass gate, Katsuki held Izuku’s hand. The mer’s fins twitched in excitement as Toshinori cranked it open. 

“Ready?” Izuku asked.

Scarlet eyes peered at him, blinking slowly, and then a sharp-toothed grin stretched on Katsuki’s face. Pumping his tail gently, the pair inched forward through the gate with caution. The mer’s earfins were adjusting constantly, listening to everything just beyond his enclosure.

“It okay,” Izuku assured him and squeezed his hand gently. 

Tall kelp swayed in the gentle current of the connected tank. Wide, striped fish darted between the fronds at the predator’s appearance. Crabs scuttled across the sandy bottom, claws raised to fend off a potential threat.

The biologist urged them forward knowing this was the part that would make or break the entire experience. Walls and walls of windows lined one side of the tank and even through the warped blur from the salty water, Izuku could see curious faces pressed against the glass. 

“Children,” the human warned and Katsuki’s attention snapped toward the ogling group. 

The mer paused in his advance, clearly unsure of the scrutiny. Izuku reclaimed his hand and swam forward to wave at the kids. A few gestures got them to step back a few large paces and then the biologists turned to the massive black mer. 

“Come on, Kacchan!” He laughed and waved.

Slowly, the hulking predator cut toward Izuku, eyes and fins constantly shifting as he ran risk assessment. Mouths hung open in awe as the school children pointed and waved, jumping up and down excitedly at the appearance of such an incredible creature.

“They can’t hurt you,” Izuku promised. “Can only watch.”

“Humans hurt…always,” Katsuki rumbled and charged the glass, stopping before he could collide with it. Three kids fell on their butts as they startled and jumped back in fear. The mer turned back with a toothy grin and a raised brow.

“Mean Kacchan,” the biologist laughed. 

He offered his hand to the mer, only for Katsuki to lurk from above and wrap his arms around his middle. Izuku laughed as he was carried through the water at a speed he could never hope to reach on his own. But then they stopped suddenly with the mer going completely still. Muscles tensed and the biologist was released unceremoniously as Katsuki inspected the glass.

Ah, they’d reached the curvature. Izuku knew this would confuse the mer.

“Deku? Why wall curve?” Katsuki asked as he felt it up.

“Tunnel where people can walk under.” Izuku explained, swimming up and over to the other side. 

With a bit of trepidation, the mer followed. “Stupid,” he grumbled, and the freckled human had to laugh at the comment.

They explored a bit more and once Katsuki was comfortable enough, he ventured farther and farther from Izuku. The mer chased schools of fish and snapped his serrated teeth at the children who watched with eager eyes. 

Izuku watched on, a sense of relief and triumph washing over him. Kacchan had come so far in such a short amount of time. He hoped the mer could return to the ocean one day, but all the observations, ultrasounds, and x-rays told a different story. It felt wrong to keep such a majestic creature in a confined space. That was the very reason Izuku pushed the board to accept his proposal. And it was going so smoothly. 

“Deku! Deku!” Katsuki shouted charging straight for him.

Izuku crossed his arms in front of his face and screamed. Memories from just a few weeks prior flashed behind his tightly shut eyes. A flood of bubbles washed around him as he breathed too fast, heart thumping wildly in his chest. But an attack never came. Instead, he was tucked under Katsuki’s arm and cradled against the mer’s body as he sped them back to the private enclosure.

The next thing Izuku knew, he was being hauled out of the water by two massive hands around his waist. He ripped off the goggles and breather, sucking in heaps of fresh air. Body trembling, the biologist rested his elbows on his thighs and cradled his face.

“What happened?!” Aizawa shouted, running over to the edge.

But Katsuki let out a rumbling hiss in warning. Gently, the mer grasped Izuku’s wrists and pulled them away from his face. 

“I’m sorry,” Izuku whispered, voice shaking. “I’m alr-”

“You’re not,” Toshinori cut him off. “Get him away from the water.”

“Deku?” Katsuki whispered and the biologist finally opened his eyes.

Izuku was surprised to see that fiery scarlet gaze filled with so much concern. The mer dropped his wrists in favor of cupping his face, claws carefully swiping away the tears he didn’t even know were falling.

“Deku scared of Katsuki?” the mer warbled.

“No,” Izuku swallowed. He shook his head as best he could with it still cradled by the mer. “No. You startled me. Just s-seeing you come at me-”

“Deku scared of Katsuki,” the mer whined sadly. 

“No Kacchan,” Izuku shouted, blinking away new tears and gripping the mer’s wrists. “I am not scared of you!”

“Be better if he was,” Aizawa grumbled under his breath. 

Katsuki rose out of the pool to bump their foreheads together and Izuku laughed through a sniffle. And then, just like two weeks before, the mer kissed his cheek, this time nibbling carefully with those sharp teeth. 

“Oh my goodness,” Toshinori gasped.

“What?” Aizawa snapped. 

“Katsuki has accepted Izuku,” the older biologist breathed.

Izuku returned the gesture, pressing a kiss to the mer’s lightly scaled cheek. “Thank you, Kacchan,” he whispered, resettling to bump their foreheads together again.

“Katsuki protect Deku,” the mer rumbled. 

“Izuku protects Kacchan,” he murmured back. “Always.”

Six Months Later

Katsuki prowled between his private enclosure and the long stretch of water that housed many familiar creatures. No faces peered at him through the glass. Too early for visitors. 

The lights were low simulating dawn. His predatory instincts kicked in as he hid in the kelp beds stalking a school of mackerel. Katsuki knew Deku would be mad if he ate them all, but if he could just have a taste…

The bright orange sailfin on his back twitched as a Blacktip Reef Shark swam past. Katsuki rumbled low, sending vibrations into the water and the shark darted away. They were harmless to the giant mer, only slightly longer than Deku was tall. Still, he didn’t like the competition for food. Okay, so he didn’t actually need to hunt anymore, but instincts were instincts. 

Sharp eyes tracked the school of fish. The mer was poised to strike from the shadows. 

He didn’t have the speed he used to. Four months ago, Katsuki got a bit too curious about the door that separated his enclosure for the Sea of Japan exhibit. For over an hour, his tail was trapped beneath the metal enforced plexiglass gate, fracturing the same vertebrae that had been dislocated in his initial injury. Izuku had been distraught when he found him later that morning. Dr. Koda poked him with a needle that made him very sleepy. When he woke, he’d been put back in that shallower tank with wrappings halfway up his tail. With red-rimmed eyes, Deku explained they’d had to put a metal rod in the lower part to stabilize his vertebrae. It affected his movement and officially sealed his fate as a permanent resident at the marine center.

With a jolt of electricity from the top of his head to the tip of his fins, he darted forward, only to halt at a massive bang against the glass. Startled fish scattered and Katsuki snapped toward the sound.

Deku glared at him through the glass. Shit, he was going to be in trouble. The human pointed harshly back toward his private enclosure. With a grumbling sigh and a roll of his eyes, Katsuki swam in the direction that was indicated.

The mer paced the length of his tank over and over until he heard the telltale beep of the security latch and scrape of the heavy door on concrete. Cautiously, he peeked his eyes above the surface, earfins twitching and splashing droplets.

“Kacchan,” Deku scolded. “You know better!”

Katsuki approached the rocky edge of the pool and hauled himself out of the water. He pointed toward the bucket of live fish that the biologist had brought with.

“How many did you eat already?” 

“None,” the mer stated.

Deku crossed his arms and jutted out a hip while raising a brow at him.

He sighed in defeat. “Two.”

“Kacchan you can’t just-”

“Katsuki hungry and no Deku to feed. So, Katsuki hunt!” The mer protested.

“You knew I was coming,” Izuku grumbled and pinched the bridge of his nose. “You know I come earlier than everyone else so I can spend time with you at the ass crack of dawn.”

Katsuki warbled and scooted closer to the biologist and rubbed his cheek against the thick cargo pants. Serrated teeth playful nipped until he spotted a smile teasing at Deku’s lips.

“Brat!” The human laughed and swatted him gently. “Come get your breakfast.” 

Deku dumped the bucket of fish into the pool and Katsuki dove immediately to chase. The hunt wasn’t nearly as extensive as it had been when he lived in the wild, but at least there were no more pathetic frozen fish that were already dead. What an insult that was!

When the mer rose from the water again, Deku had taken a seat at the edge of the pool. His boots and socks were removed, pants rolled up, so he could dip his feet beneath the surface. 

Katsuki dove down again, a playful smirk etched on his lips. Scarlet eyes tracked the gentle back and forth as Deku kicked his feet through the salty water. Darting upward, the mer attacked his toes, enjoying the screech his favorite human let out.

“Kacchan! Stop stop!” Deku laughed and kicked even as his feet were trapped by dangerous, but gentle, claws. 

“Deku in Katsuki territory. Whatch out!” The mer snapped playfully with a growl.

“Okay, okay, I get it,” Izuku giggled and dragged his bag closer. “I shouldn’t let my guard down even if we’re close now.” 

The human pulled out a plastic container Katsuki recognized from other times spent together. It smelled fresh, but then Deku had to go and ruin it by dumping that salty brown stuff all over the rice and rolled fish. He made a face and Izuku laughed.

“It’s not that bad.”

“Terrible,” Katsuki hissed. “Ruin fish.”

Deku popped the whole sushi roll in his mouth, chewing so his freckled cheeks puffed out comically. He hummed dramatically, “Mmmmm, delicious.”

“Brat,” the mer scolded back with a gentle nip to the biologist’s big toe. 

Katsuki pulled himself out of the water and cuddled up to Deku. He dwarfed him, something he teased Deku about often. Readjusting to lay on his side on the soft moss-covered rock bed, the mer nuzzled his head into Izuku’s lap and crooned.

“Did you miss me, Kacchan?” He asked softly, hands setting aside his own breakfast in favor of carding them through coarse blonde spikes.

“Always miss Deku,” Katsuki rumbled. His stomach flipped as fingers nudged in just the right spot at the base of his skull. 

Months ago, the thought of being anywhere near a human repulsed him. Katsuki stretched an arm over Deku’s thighs in the approximation of a loose hug. He may never return to the wild, but that was okay. Katsuki had found a new home. One with an abundance of food and entertainment. And most importantly, Deku. The mer knew, given the choice to return to the ocean or stay with the freckled biologist, he would choose Deku every time. 

Katsuki crooned softly when he felt the human bend over him to press a kiss to his forehead.

“Love you,” Izuku whispered against his skin.

“Katsuki love Deku,” he warbled, nuzzling closer. He would always choose Deku. Deku was home.