I haven't written fanfiction since 2017, but how could I resist mermaid Jirou?

This plot is based on an RP I did with a friend on Amino. Alex, if you're reading this, thank you for blessing me with this idea, and I'm sorry for taking a year to actually write it. Ana, my gal pal, beta read this for me, so it's not as bad as it originally was.

Thank you guys for reading, and I hope you stick around :)

There's always been something about the ocean that drew Yaoyorozu in. Maybe it was the fact that she grew up on the beach, or the calming sound of ocean waves that never failed to lull her to sleep when she opened her windows at night. It's possible this is something that everyone experiences- the fascination with the unknowns of such an unexplored world. As a child, she used to dream of the dark, underwater world where she would sink down farther and farther, but there never seemed to be an end. She would stay floating, drifting deeper into another world until she awoke. It was never scary, there was never any fear of drowning or losing air, not even the sharks fazed her as they circled her small figure. However, there was always an ache when she'd find herself laying in her bed, like something was missing. On those days, she always had a tune in the back of her mind. It sounded so familiar, but she couldn't draw it to the front of her mind no matter how hard she tried.

It's been years since she's dreamt of the water and now she regards the experience as something from her childhood. It isn't unusual for kids to have strange dreams, even lucid ones, so she never put much thought into it. Besides, she's in high school and there's a lot of much more important things to be figuring out. Social skills have never been her best asset, but she always manages to surround herself with a few people she likes. Last summer, she even got herself a boyfriend. Todoroki Shoto, a friend from elementary school who she practically grew up with. Their families are close and both sets of parents seem to approve of their relationship. Life has been treating her well. She's content with how things are, and she wouldn't wish for them to change.

Though, sometimes the unordinary sneaks up on people.

The breeze is warm and she can feel summer rolling in on her way home. The house by the beach isn't far from the private school she attends, and while she could get a ride home, she prefers the fresh air and light exercise. She's careful not to scuff her school shoes, even though she has extra pairs. It's just a regular day, and she walks up the driveway to her house as usual, opening the door, then freezing. The sound she hears is distinct, but seemingly far away. She can hardly tell if it's someone's voice or not, but it strikes a chord. The melody sounds so familiar. Something stops her from digging too far into her memory to find the origin of the strange nostalgia. It's probably just someone playing music after all, so she heads inside to fix herself something to eat. She finds herself falling into the same routine as every other day, nothing else seeming peculiar for the time being. After all, nothing odd ever really happens on a school day.

She heads to her room after eating, planning on changing out of her uniform and into something more comfortable to lounge in. With her family being quite financially… comfortable, she's never had any concerns when it comes to space. Her room has always been a place to relax, decorated however she wanted. She's changed the theme of it many times in her life, but she's kept the same gold and white color scheme for years now. She prefers to keep things simple these days, unlike her past self.

She pulls some lounging clothes from out of her dresser, stopping for a moment to admire the old trunk placed at the foot of her bed. It holds the extra stuff that doesn't need to be displayed in the area, along with some of her most prized possessions. It's nothing that would catch the eye of anyone, and sometimes she even wonders why she keeps so many seashells after all these years. She lives on the beach, it's not like there's a shortage of them, but she swears that some of them she's never seen anywhere on the beach, or even in the gift shops aimed at curious tourists who come through the city. Ever since she was a child she would play this game with her mother, swapping out toys for beautiful ocean artifacts on the shore. Her parents used to insist it was a mermaid who she was exchanging gifts with, and it brought her a childish type of joy. Of course she's now figured out that the story was as real as the Easter bunny, but it still leaves her with a fluttery feeling. She hasn't talked about it with them since she stopped leaving her things on the sand to be swept away. She probably lost a lot of toys to the sea, her parents must have spent a lot of time placing things for her to find. She isn't sure how they managed to keep them from getting swept away.

Next time they're home, she'll bring it up. It'll make all three of them laugh. It's been a long time since she's laughed with her mom and dad.

Before she can get too sentimental about it, she changes her clothes and leaves her uniform in the basket for dirty linens, heading back downstairs. She has some school work to do, as always, but she prefers to take a break and settle down after classes end before completing it. She has all the free time in the world, it seems, so there's no harm in it.

She glances out through the sliding doors as she reaches the bottom of the stairs, eyes catching a quick glance of color. She does a double take, squinting slightly to see the object better. She can't make it out clearly, but from what she sees, it seems bright and multicolored, resting on the shore, just far enough to not be swept away by the waves. Her curiosity gets the best of her and she steps out onto the back porch, not minding the feeling of her bare feet against the smooth wood. Continuing to walk towards the source of her confusion, she steps onto the sand and quickly makes her way over.

It's just a child's toy, and when she first recognizes it as such, she brushes it off. The longer it sits in her mind, though, the more weirded out she becomes. This is a private beach, and as far as she knows, no children have been at her house as of late. The appearance of it also rings a bell, and she swears she had something similar growing up. It's typical for things to wash up, but something that was swept away so long ago? It's… not impossible, she supposes. Maybe it means something. She picks it up and watches it as if it may reveal some sort of hidden message. Of course, it doesn't. Eventually she returns inside and doesn't think of it.

That is, until more show up.

Momo isn't a superstitious person, she tends to think more logically rather than getting paranoid about something she considers out of her control. But this is something she can't help but linger on. Every day for the past two weeks, she's come home to find an old, pretty worn out toy on the beach. Some of them she vividly remembers being part of her collection as a kid, and she's positive they're the ones she left as an exchange for pretty objects from the ocean. One time was unlikely, this is just… for lack of a better term, freaky. No matter how hard she tries to dismiss the thought of it, it keeps reappearing in her mind. She can't find a rational reason for this to continue happening.

Her parents won't be home for a few more weeks, she'd gotten the call from them the previous night. She couldn't bring herself to be too upset about it, not anymore. It's not like she'd be able to tell them, anyway, she's sure they would think she's crazy.

She comes home from school, not bothering to eat or get changed this time. She heads straight for the back after pulling off her shoes and socks, not wanting to dirty them. She's a bit exasperated, just wanting to collect the new plaything left in the sand for her. It's beginning to get on her nerves when she doesn't fear it. Sure enough, she locks eyes with a red block outside, floating in the shallow water. Fantastic.

She trudges across the beach, kneeling down in the water, just close enough to grab the object. She reaches out, but when she grips the toy, she finds it needing a bit more force than expected. The toy pops out of the sandy water, along with a small hand. She shrieks, falling backwards and splashing water onto herself. Struggling to get away as fast as possible, she finds her footing and backs up quickly, hearing racing in her chest.

When her eyes focus again, she finds her eyes meeting another pair, bright like amethyst. The girl looks tiny, short, messy locks of purple hair framing her face. Her eyes are sad and teary, and if Momo wasn't so frightened, she'd feel bad.

The stranger moves closer and Yaoyorozu moves farther back, hands shaking as her brain tries to form a coherent sentence amidst the panic. The smaller girl speaks, voice soft and shaky, yet slightly deeper than her own. At first, Momo thinks it's a different language, but she's able to translate the heavily accented speech after a moment.

"You angry… me." The purple haired girl questions, sounding a bit torn up. "Why?"

As soon as Momo realizes that the girl believes she's angry with her, she sees movement behind her. A tail rises out of the water, shiny purple scales reflecting the sunlight as it splashes some water around it. Dark eyes travel along the limb and find it connected to her new acquaintance. This girl is…

It's then that Yaoyorozu's eyes roll back, fall cushioned on the sand once she passes out.