This was supposed to be a one-shot, 5k words at most. It rapidly spiraled out of control and now I have another 20k words ""one-shot"" I separated into a mini-fic for ease of reading. I,,,, got carried away,,,,,

also i fuckin' hate writin' summaries. they can go die in a hole. can't the reader just telepathically Know what the plot entails without me tryin' to spin a shitty little description, huh???

i'm always very guilty of just leaping straight into the fun part of the story when writing, so i decided to step out of my comfort zone with this fic by adding more exposition and description, but, uh,,, yeaahhh that led to me writing 20k words....... oh well, lol. it was fun!! and also wow can you believe this is actually finally a New Fic rather than one i had lying around in my drafts for years... wild. look at me bein' all productive in quarantine, i'm proud

Song I listened to pretty much the entire time whilst writing this whole fic: 

(plus this at the end of writing)

take care of yourselves, and i hope you enjoy <33

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Summary:

Izuku has always known the importance of secrets, long before All Might passed One for All onto him. With a merman father and a human mother, his life is certainly unusual, even in the peculiar age of Quirks.

And for a mer like Izuku, a school trip to the ocean seems like paradise!

...but, of course, trouble follows him wherever he goes. Damn it - can't he just have a relaxing break with his friends without getting attacked by villains for once?!

CW: Blood & Injury, Canon-Typical Violence

~

Chapter Summary:

Izuku yearns, has a secret, and plot convenience dictates that these two things will soon clash.

~

Izuku closed the door to his dorm room, leaning back against it with a tired sigh. It had been a long, stressful day of classes and sparring, and both his brain and body were exhausted. He straightened up and turned around to lock the door, then sleepily padded deeper into his room as his scarred hands worked on loosening his scrunched tie.

Warm, sunset hues pooled through the balcony doors, spilling amber across the carpet and painting over his feet. Izuku tried the handle to check it was locked, then pulled the All Might curtains together, plunging his room into near-total darkness. A faint light glowed through the fabric and shone around the edges of the curtains, allowing him to navigate safely as he got changed into his pyjamas.

He snatched a water-bottle from his desk and sat heavily on the edge of his mattress. Green eyes furtively examined his surroundings once more, lingering on shadowed spaces and pausing on both doors whilst he strained his ears to listen for any sound. Aside from the faint chatter of his fellow students on different floors, and the occasional pad of footsteps passing in the corridor, there was nothing – he was alone.

Izuku brightened, eagerly unscrewing the bottle and carefully pouring a few droplets into the cap before placing the bottle onto the floor. He tugged up the hem of his shorts to bare more of his thigh, cautiously scanning his room once more, then focusing on slowly tipping the cap sideways. Lukewarm water dripped onto his thigh, pooling out and glittering like dew on his skin.

It was like a new muscle had been connected to his mind as the water seeped into his leg. He screwed the cap back on the bottle and settled more comfortably back into his bed, kicking his feet up onto the covers. Izuku focused on that new feeling and tensed the muscle, observing with giddy glee as his skin melded together and shifted into a greenish hue. Soft sparks glittered as smooth scales slid into place, chasing down his body and flicking up into a wide fin.

A large fish tail had replaced his legs. All that remained of his shorts was a band of fabric around his mid-section, covering where skin blurred into scale and joined with some frilly fins circling his waist. Glimmering viridian scales concealed powerful muscles. The green reflected with subtle rainbows like spilled oil, lightening as the tail continued on until it was a soft lime colour at the tips of his fin. Deceptively delicate membrane stretched between the fin's ribs, bordering on translucent when flexed out, but currently opaque in the curves and folds of its relaxed state.

He ran his scarred hands over the smooth scales, revelling in the soothing sensation. His palm caught on an uneven patch, and he paused, deftly urging the shed scale loose and pressing it between the length of his fingers as he continued searching. A few more were collected before Izuku was content, and he raised his hand to admire the pretty scales. They varied in size and shape, with the ones collected closer to his torso being about the same as a guitar pick, but growing smaller and more rounded towards his tail-tip to allow for more movement. Each one shimmered ethereally like a slice of gemstone.

Izuku twisted and rolled onto his stomach to hang over the edge of the bed and peer underneath, one hand fumbling before sliding a shoebox out. He took off the lid to reveal a treasure trove of shed scales – he'd been storing them since he moved into the dorms, too nervous about people seeing them if he tried to throw them out – and he tilted his palm to let the scales tumble inside. They plinked like pebbles upon landing, and he reached out to grab the box with both hands, gently jostling it. A sound like the ocean arose as the scales rubbed against one another. He closed his eyes and lost himself in the noise for a moment.

It brought back vivid, comforting memories of rushing waves crawling over sand and pebbles, bubbling pale foam painting the edge of each wave as it crashed in, no matter how big or small. The feel of soft sand shifting under his feet as he clumsily ran across the beach, passing tangles of seaweed and shells and driftwood of the last tide, transitioning to the solid sand, darkened with water as he approached the shore. Dips and divots in the hard sand cradled tiny pools that he splashed through, coming to a halt just a pace away from a flat wave that spilled over the land, thin and clear enough to be a sheet of glass. Sunlight danced on the surface of the sea, glittering like a million diamonds slept below the surface. Salty air filled his lungs, fresh and cold and bitter on his tongue, but utterly intoxicating. Water lapped playfully at his toes before receding with a gentle growl, and he automatically moved to chase it, running towards the newborn waves that barely reached his ankles, moving onwards and feeling cool water press against his skin, coaxing him deeper and deeper until he was forced to slow to an agonising wade, and the sea wove around his chest. A wave arose, tall enough to cast a shadow over him as it dragged him closer, then it slumped heavily over his head, plunging him into darkness. He let himself get tumbled around beneath the surface, focusing on the familiar call and feeling new features spring up over his body. With a powerful flick of his new tail, he launched deeper underwater, fingers brushing against the sand and teeth bared in an excited grin with water combing through his hair and ghosting past his gills and easing over his fins – and the ocean embraced him.

Izuku blinked, and the illusion was gone. He put the lid back on the box and slid it back into the shadows, then heaved himself up onto his back to slump back against his pillows, tugging the blankets over his tail and letting out a satisfied sigh at the wonderful, soft sensation. There hadn't been a free moment to properly visit the sea ever since he met All Might, and he missed it so much it hurt.

But, he was finally following his dream, he had so many friends, and he had a powerful Quirk – what more could he ask for?

Izuku rolled onto his side and curled up, pulling the blankets to his chin and sinking into memories of sand and sea. The homesickness remained.

*

The story of his parents was one he knew by heart.

Hisashi, a merman, and Inko, a human woman.

Against all odds, they met, fell in love, and had Izuku.

Merfolk tended to remain hidden in the ocean. Initially, it was for their own safety, as humans were dangerously fascinated with researching everything. The few merfolk that dared venture ashore sparked up rumours and tales that lasted centuries, making it even more perilous to swim too close to the surface for fear of being caught by fanatics.

Then Quirks arrived. With more and more humans gaining strange powers, merfolk were less oddities and more normal. They stepped onto land more often, and no-one batted an eye at the sight of someone growing a tail. Being able to shift into a human form wasn't something every mer could do, and it was a tedious process for those that could, since even a single drop of water could have them involuntarily regain a tail. Enough humans and merfolk had children for the shifting trait to become more common, and some of them even gained a Quirk.

That was the case with Hisashi. He had enough control over his human shift to spend more time on land without worrying as much, and he had inherited a fire-breathing Quirk from his ancestors – which wasn't particularly effective underwater, and he wasn't keen on using it on land, either, because it dried out his throat. On one of his adventures through Tokyo, he met Inko, and he thought she was the most beautiful person he'd ever seen, human or mer. They went on dates, fell deeply in love, got married, and had Izuku.

It became clear very quickly that Izuku had inherited the same mer-shifting ability, except they were stunned to find it wasn't like Hisashi's, or any of the other merfolk's – although he still needed contact with water, he didn't automatically shift, nor appear to struggle to hold his human form, like Hisashi. Instead, he changed by choice. If he wanted his mer-attributes to appear, they would, but if he wanted to stay human, he would.

He was a wonder, and both of them adored him, but...

No matter what he tried to insist, Hisashi wasn't comfortable on land. They tried to compromise, trying out bathtubs of salt, or visiting the ocean when they could, but it wasn't enough. With the addition of his Quirk, he was drying out too quickly, and it was taking a huge toll on his health.

Eventually, although neither of them wanted to, Hisashi and Inko separated and went their own ways. It was better for the both of them, and Izuku stayed on land, but visited his father in the ocean as frequently as he could as he grew up, spending holidays and weekends and occasionally visiting between school hours, and even though the caution of humans remained, Hisashi didn't mind swimming to shore to meet his son.

That same caution coerced Izuku into making the decision of keeping his heritage and ability quiet. He didn't want to be the reason that his mer-family were put in danger if someone found out that merfolk were real, just because he was careless with his power.

Even when diagnosed with the death-sentence of Quirkless, he remained quiet. He honed his mer side until he could choose which attributes to shift, allowing him to separately gain his gills, or fins, or tail. It wasn't like it made much of a difference to his everyday life, but it gave him something to do – something to be proud of.

Meeting All Might and training to receive One for All and get into UA meant he barely visited the ocean. Sure, cleaning the beach placed him right next to the water, but it wasn't a place he wanted to try swimming. With all the rubbish and sharp objects washed ashore, who knew what sort of toxicity had bled into the sea?

It was taunting him with its inaccessibility, but he pushed through, like he always did, banking on the hope that, once he got into UA – because he would, he was going to get in, he couldn't let All Might down – then things would've calmed down.

And then the villains attacked. And again. And again. And-

Izuku was tired. He loved his new life, and all the opportunities that came with it, but being deprived of the ocean was taking a toll on him. It wasn't as bad as it was for his father, but it still hurt, like half of him was missing. With them being stuck on campus all the time for their safety, and having to make a request to be able to leave– Well. It just wasn't viable.

Still, he stayed hopeful. Maybe tomorrow, things would be better.

Maybe tomorrow...

*

"The school has organised a trip for the students who scored highest in the exams as a reward," Aizawa drawled like it wasn't the most exciting thing the entire class had heard all week. "A retired hero with a boat has offered to take the top six students on a tour around the coast, and teach them how to drive a boat."

Izuku was practically vibrating in his seat. He had scored fourth!

"Don't think it's going to be all fun and games. It's only for two days, and you will be given homework to do whilst on board so you don't fall behind in your classes. You will learn the dangers of the ocean and how to read the currents and weather to avoid getting hurt." Aizawa lazily scratched at his stubble, taking a painfully long pause that had everyone squirming. "Oh, yeah. All Might will also be accompanying you."

It took everything in Izuku to not shriek. Not only was he going to be on the ocean for two days – two whole days! – but he was also going to be spending time with his friends, and his mentor!

The groans and pleas from his fellow classmates made it very clear how unhappy they were with missing out on such an opportunity. Kacchan was slouching smugly back in his seat, nearly bumping into Izuku's own desk – he had scored third. Perhaps it would be a little nerve-wracking to know he was going to be stuck on a boat in the middle of the ocean with Kacchan for so long, but he was willing to make that sacrifice; besides, they had been on much better terms since the secret of One for All had been shared. Kacchan had only punched Izuku, unprovoked, once in the past three days! That was a new record!

But, if Izuku remembered the scores correctly – and of course he did, because he wanted to know how much he had to improve to reach the top, because he couldn't slack off! – then Todoroki and Asui had snatched the last two places, and Iida and Yaoyorozu had claimed the top two spots. That meant he also had friends who wouldn't punch him in the face if he got too close, and it was going to be so much fun!

"You will be leaving this afternoon. Please pack your bags at lunchtime and be prepared to go at 4pm, otherwise you will be left behind."

Izuku was already planning what he needed. Obviously he needed at least one change of clothes, perhaps two – or, hm, maybe three, just in case something happened – and would he need to take his school uniform or his hero costume? Did he need to bring a swimsuit, or towels – and he must need soap and shampoo, right? Was there even a shower? Boats must have showers, surely? Oh, he should take his notebooks! Maybe he could start a new one, dedicated to everything he would learn on the trip, and then he could show his other friends who couldn't go, because it wasn't fair that they were missing out on skills that could be super important as a hero. Which reminded him; who was the retired hero they would be learning from? They were probably a nautical-themed hero like Selkie if they had retired with a boat and knew so much about the sea, but Izuku couldn't think of any retired sea-heroes, and now he really wanted to research to find out, because then he could possibly prepare himself for what they were like so he could make a good impression and-

"Midoriya," Aizawa cut in flatly, and Izuku jolted, slapping his hands over his mouth and sinking down in his seat as his classmates snickered. "You're only allowed a backpack for all your items, because there's not enough room on the boat for whole suitcases of things. Sleeping bags will be provided. Two sets of clothes is more than adequate. If the sea is safe enough, there is the possibility of swimming, so bring a towel and a swimsuit. Yes, there is a shower. You'll likely only need to wash once, so just bring travel bottles of toiletries. Be aware that anything you bring will likely get damaged in the salt-spray."

"Thank you, Aizawa-sensei," Izuku mumbled, thoroughly embarrassed.

"Kero, I'm curious about the retired hero too, Aizawa-sensei," Asui spoke up from across the class, raising her hand to talk. "Are we allowed to know who they are?"

"Her hero name was Neptune, and she retired over a decade ago, so it's not surprising you don't know of her," the teacher explained.

Neptune, Neptune... It sounded faintly familiar. He'd definitely read something about a Neptune at some point...

"Why'd she retire?" Kacchan asked gruffly, hunching over his desk again to glower at the front of the class.

"Oh! Neptune-san!" Izuku exclaimed as the realisation hit him. "The Galloping Hero: Neptune-san. Quirk: White Horse! She can create and ride horse-shaped waves, and after graduating from Shiketsu, she specialised in sea rescue due to her fast speed and attunement to the ocean!" He frowned slightly, recalling the reason for her retirement. "There was an incident with a villain who took an oil rig hostage. She went to help out, but during the fight, the rig started to collapse, and she prioritised getting the civilians to safety on the boats, but... some of the debris fell on top of her... It crushed her arm and both her legs, and they had to be amputated. They were replaced with prosthetics, but she needed her limbs to properly control her Quirk, and with only one arm the White Horses weren't strong or stable enough to save people anymore... So she had to retire early."

"That's terrible," Uraraka murmured, and by the sombre atmosphere, everyone shared that sentiment.

"Now she volunteers with the coastguard in her free time and patrols the coasts. It's often thanks to her that other heroes get early warnings of potential villain attacks or civilians in trouble," Aizawa informed them brusquely.

"Staying busy and continuing to help people like that, even after such a bad accident... That's so manly!" Kirishima exclaimed, gaining a few laughs and successfully lightening the mood.

His dark eyes flicked to the clock, and he promptly pulled his yellow sleeping bag out from behind the podium. "That's all. Don't be too loud for the rest of homeroom."

~

i forgot mermay was a thing until i saw some art and thought "ah i wanna do mermay this year, but idk if i have anything to- oH GOD I FORGOT ABOUT THAT MER PLOT I WAS GONNA WRITE FOR MERMAY HELL YEAH"