Marine biologist Kirishima who is at a fish market in town where he sees mermaid Katsuki trapped in a too small tank as some kind of side show attraction. Katsuki's orange tail is dull and his skin is ashen and there's a painful looking muzzle on the mermaid's face.

Kirishima approaches the tank and its obvious how sick Katsuki is from improper care and there are bruises all over him. He knows he needs to get the mermaid out of the tank but he also knows he's not going to paying the money for him. 1. It would just give the bastard-

-a reason to go get another mermaid and abuse them and 2. Kirishima wouldn't be able to afford the price.

So he waits until nightfall. Waits until the park is market is closed and sneaks in. He doesn't really have a plan other then getting the mermaid out of that tank.

Hes strong enough that he can lift Katsuki from the tank and carry him all the way to the parking lot. It says a lot that there isn't any security around Katsuki. Katsuki is too weak to fight but he does have sharp claws that scratch weakly at Kirishima’s arms.

He ignores the pinpricks of pain because he knows the mermaid doesn't understand Kirishima is trying to help. The way the muzzle keeps the mermaid's mouth clamped shut only allows for weak distressed whines to be heard and it breaks Kirishima’s heart. Mermaids have beautiful-

-songs that should be appreciated. Kirishima wonders how long its been since this one has been able to sing.

From the state he's in, its clearly been a long time.

Kirishima gets Katsuki back to his home, which is right on the ocean with its own dock. He knows that he should release the mermaid but he can't not until he's sure that the injuries aren't life-threatening.

So he takes the mermaid to his lab where he has a huge pool.

The seawater in it is filtered and fresh, it's big enough that Katsuki will be able to swim around in it and rest comfortably. The mermaid tries to fight him and weakly reaches for the ocean. "I'll get you back in the ocean," Kirishima tells him, "when I'm sure you're healed."

Those ruby eyes are distrustful, but it's not like the mermaid can fight him.

As much as Kirishima doesn't want to, he leaves the muzzle on while he performs his initial examination. Just in case the mermaid tries to bite him. He speaks quietly, telling the mer everything-

-he's doing before he does it and that respect seems to be enough to have the mer relaxing just a little.

The exam shows missing scales on the mer's orange tail, lashes on his back, and a bad lung infection. The infection probably came from that grimy water.

Kirishima will have to try antibiotics to mitigate infection and that could take weeks to heal. All of which he tells the mer.

Sad red eyes blink up at him and whines at those words. Tears in his pretty eyes. "Hey, I'm sorry, please don't be sad," Kirishima says.

"I promise, I'll get you home as soon as I can." Then he removes the muzzle, throwing the offending object away from them. The bruising on the mer's throat is deep and ugly. "Try not to speak," or sing, he wants to add but doesn't, "we have to let your throat heal."

The mer gets even sadder but he nods.

His exam also showed that this beautiful mer is an omega. They're considered extremely special to their pods and are protected with terrifying force. Kirishima wonders how this one ended up all alone in some fisherman's display tank.

Kirishima starts the rounds of antibiotics and then helps the mer into the pool.

He's not able to really swim well right now, but the pool leaves enough space that Katsuki and spread his tail out. It's a vast difference from his prior accommodations.

Mermaids, unless taking a human form as is a rumored possibility, can't speak the human language. They can understand just fine but communication is difficult. Kirishima only learns Katsuki's name after bringing him a notepad to write on. That, however, is the extent of what-

-Katsuki is able to write. Everything else is just guesswork.

It's fine, Kirishima thinks he's done a good job of trying to understand Katsuki. Well, it helps that the mer flicks water at him if he doesn't figure it out.

Each day, Katsuki begins to heal. His back is better, the lashes fading into thin scars and his tail begins to grow the missing scales back. The bruising on his throat is deep but it too begins to get better.

Katsuki is able to give dolphin-like clicks now.

Kirishima can't understand the clicks but the pitch helps him discern if Katsuki is angry, happy, or sad.

The thing is, Katsuki is always sad. Always looking toward the ocean with so much longing and his pretty eyes always mournful.

It makes him want to release Katsuki sooner, but he can't. Not until the lung infection is gone. If Katsuki were to go out there, he could die without the right treatment.

Katsuki understands that but it doesn't help the longing in his eyes.

Three weeks after Kirishima brought the mer home, he hears it. It's the clicking but different. Like wind chimes in the breeze.

When he peaks into the pool room, he sees Katsuki leaning on the edge. He's singing. It's beautiful and hypnotic and so so sad.

Kirishima sinks down on the floor to listen, because what else can he do? All he wants is to help the mermaid but his help is also hurting him. It's keeping him away from where he wants to be.

So he sits on the floor and listens to Katsuki's beautifully sad song.

He must fall asleep because when Kirishima next opens his eyes it's to see three figures in the pool room. Body jerking, Kirishima shoots up.

What if that fisherman found him? What if he's come to take Katsuki again? Kirishima won't let that happen to the mer.

But he doesn't need to worry because the singing stops. Katsuki looks at the figures and excited happy clicks sound in the room.

One of the figures runs forward and suddenly Kirishima can see that all three figures are very wet and very naked.

Scales decorate their bodies in a similar fashion as they do Katsuki's own pretty orange. The one who runs forward, another blond, is covered in golden yellow scales.

He wraps his arms around Katsuki's shoulders and Katsuki does the same. They rub their noses together-

-the clicking gettings softer but no less excited. The new blond, in this human form, can't click but there are happy tears on his face. "Kaachan, Kaachan, we've missed you. We thought you were gone forever," he says.

The woman, with bright pink hair and pink scales-

-comes forward next and turns Katsuki's face to hers. "Hi Princess," she says. "I'm so happy to see you." Then she's kissing him and Katsuki's tail is flicking excitedly in the water.

The final one, another man with black scales, turns his attention to Kirishima.

A snarl is on his face and he moves between the pool and Kirishima. An alpha, both him and the woman, the way they hold themselves tells Kirishima everything he needs to know.

And right now, Kirishima is the human who this mer sees as a threat.

Kirishima backs up until his back is against the wall. "W-wait! I-"

The alpha growls, if he were in his mer form there'd sharp teeth flashing, and takes a threatening step forward.

But he doesn't get further. Urgent clicking and splashing stops the alpha in his tracks.

He turns back to look at Katsuki who is looking at them with wide eyes. The alpha huffs and turns away from Kirishima to go towards the omega.

He takes Katsuki's chin in his hand and gently lifts it to look at his neck. The bruises have yellowed with time as he heals.

The alpha's fingers are gentle as they run over the marks "Not him?" he asks.

Katsuki clicks again, his body relaxing.

The yellow mer turns to Kirishima. "We want to take him home now." His voice is thick as he speaks.

Kirishima shakes his head. "Y-You can't."

The she-alpha snaps her head towards him, her eyes flashing. "And why not?" Oh God, she's so angry.

"H-he has a lung infection. I've got it down and it's better but if he leaves now it'll come back. He'll die out there."

Yellow whines and runs towards the steps and up to the platform. He jumps into the water and tangles his long eel-like tail with Katsuki's pretty orange one.

Katsuki lets the other mer hold him, burrowing into the other's arms as they click happily together.

The woman doesn't bother with the platform. She jumps up, grabs the sides of the clear pool walls, and hoists herself into the water.

Eight pink tentacles wrap sprout from where her legs once been and she's immediately wrapping them around her mates and pulling them to her.

The black mer takes the steps, and with his feet in the pool. Katsuki swims up to him and presses his upper half into the other's lap. He smiles at the blond and leans down to kiss his forehead. "We've missed you, Katsu," he says.

Katsuki clicks and tries to snuggling closer.

With nervous steps, Kirishima walks up to the platform. "You're not going to join them?" he asks.

"I imagine communication will be easier if you have a translator." He looks at Kirishima, the soft look he'd held a moment ago gone. "Humans never help us. Why did you?"

"I'm a scientist," Kirishima says, "I...I couldn't stand seeing him in that tank. He was dying and I couldn't let that happen."

"I am Hanta," he says. "That is Denki and that is Mina." He nods to the yellow and pink mers leaning on the edge of the platform next to him.

"Kirishima-Uh, Eijirou is my first name." Mers don't have as formal of a naming system as humans. They just prefer their given names. He takes the spot next to Hanta and watches Denki gently comb the tangles from Katsuki's hair. "What happened? How did he end up there?"

As soon as he asks the question he regrets it. Looks of shame cross both Mina and Hanta's faces. "We weren't there," Hanta says. "We were hunting and Denki and Katsuki were in our cove. Hunters found our home and they took him. Denki was hurt badly but he managed to hide."

Mina clicks and one of her tentacles smooth down Katsuki's tail. "He's been gone for nearly a year," Hanta says. "We thought he was dead then we heard his song."

Katsuki pushes his upper half up and Hanta smiles as he leans down to kiss him. They're beautiful together.

Part of Kirishima is jealous, he'd be lying if he said he wasn't falling for the pretty mermaid he'd rescued, but he squshes it down. Katsuki's been through enough and he deserves to have his pod back. "Join them," he tells Hanta. "I have to get more antibiotics-

-so I'll be gone for a little while."

Hanta looks at him. "Does anyone else know he's here?"

Kirishima shakes his head. "No, it's just me here." His only friend, Tetsutetsu, was transferred to another lab on another island a year ago.

Hanta nods. "When you return I will go hunting. We will earn our stay here."

"You don't have to. I can provide enough fish for you all while he recovers."

"You are healing our mate. We will hunt for him...and for you to thank you."

Kirishima suspects arguing will lead him nowhere so he doesn't bother. "Here, I'll show you how to use some of the equipment. He hasn't had flairs since I first started treating him but just in case I'd rather you know."

Hanta's tail is reminiscent of an orca's black and white coloring. He's by far the largest of the four mers, though Mina is by no means small. He wraps himself around Katsuki who immediately presses into his hold.

Despite the longing pain in his heart, Kirishima smiles.

Katsuki looks so happy to have his mates with him, and they all fit so perfectly together.

When Kirishima returns, Mina is now holding Katsuki close. Her tentacles running up and down Katsuki's form in some sort of imitation of a massage. Her hands frame Katsuki's face and she lovingly presses kisses against his lips and cheeks.

Katsuki's face is slack, body loose as he lays there in the alpha's hold. Denki is swimming in languid circles around the two while Hanta watches with a soft look on his face.

Beautiful. All four of them look so right and so happy. Kirishima almost feels like an intruder.

The closer he gets, the more he's able to hear the low humming tune coming from Mina. She's singing to Katsuki, a mating tune if Kirishima has to guess.

Now he really feels like an intruder.

Denki is the one who notices him. He tugs on Hanta's arm and the orca mer turns to look at Kirishima. Hanta smiles lightly and kisses Denki and sends him over to their other two mates.

The blond settles on the sand next to Katsuki, molding himself to the orange mer's side.

Hanta swims to the surface, his tail melting and reforming into human legs. Kirishima wonders if the change hurts them.

"I didn't mean to interrupt," Kirishima says.

Hanta shakes his head. "You didn't. Mina won't stop until's she's happy."

"What's she doing?"

"Our kind, especially our omegas, thrive on touch. Katsuki's been without contact for almost a year," he looks sad as he says it. Like he blames himself for it. "She's trying to make him feel better."

"Is...is it working?"

Hanta looks back at the pool. Mina's singing hasn't stopped and Denki's own hire pitch has joined the chores. "I think so," he says. "It is good it was us. Had someone else done this, he could have died."

Kirishima has so many questions but doesn't ask them. "C-can I help?"

"You already have." Hanta reluctantly turns away from the pool. "You saved him. We have him back because of you. Thank you."

Kirishima rubs the back of his head. "I'm just I could help. Will being in the ocean help him more?"

Hanta nods. "So will mating."

Kirishima chokes on air. Right. Mers don't see any problem with sex being such an open subject. That's a purely human problem. "Ri-right."

Hanta grins toothily at him. "I am going hunting. I will be back soon."

Kirishima watches him go before heading to put the antibiotics in the little medicine fridge. He grabs the next dose of Katsuki's meds and heads for the edge of the pool's platform.

In the next few minutes, Mina surfaces with Katsuki leaning against her side.

Katsuki blinks blearily at him, a small smile curving his lips. Kirishima loves his smile. "Alright, read, Katsu?"

The mer nods and lifts his arm from the water. Kirishima injects the needle into Katsuki's skin and presses the plunger down. Denki bares small fangs at the-

-needle but he doesn't try anything. As soon as the needle is pulled from Katsuki's arm, Denki is pulling Katsuki to him. They click at each other, Katsuki clearly trying to calm the other down and it seems to work.

Denki gives him an apologetic look, though he doesn't-

-release the desperate hold he has on the other omega.

Mina brushes a hand through Denki's hair and kisses his neck. She clicks at the two omegas and Denki nods as he brights Katsuki back below the water.

Mina uses the edge of the platform to pull herself away onto it.

Like Hanta, her tentacles also melt into smooth legs. "Sorry about Denki, he doesn't have the best track record with those things."

Kirishima nods. "I'm sure." Unfortunately, most of the knowledge humans have about mers is from kidnapping and experimenting on them.

The lab Kirishima works for doesn't do that. They've worked hard to study them humanely, it's why he decided to work for them. "I promise, it's only medicine."

Mina nods, human legs kicking in the water. "I'm sure it is. Katsuki doesn't trust easily. Took months of-

-courting for him to let me and Hanta near him and Denki." She smiles fondly at the memory. "It just made us love him more."

Kirishima settles on the platform next to her. "Does it hurt when you change?"

"It does when you first learn, but over time it's as easy as breathing."

She kicks her legs up and stares at her foot. "Kinda ugly though. My tentacles are better."

Kirishima laughs. "Does Katsuki know?"

"Yep! He's the one who taught us." She drops her leg back in the water. "Katsuki's one of the Gifted. Very rare and very strong."

"Gifted?"

"Magically gifted. His kind are able to use magic all around them. It's not battle magic, but the kind you can find in the soft places of the ocean. He can from it into something." She leans back on her arms. "That's why humans took his scales too. To use in potions."

Maybe he doesn't want to know the answer to this question but he asks anyway. "What kind or potions?"

"Lust potions. Katsuki's a Siren. His song is the most powerful, add that to being a Gifted and it makes him...terrifying." She looks happy about that.

Then her smile fades. "We chose our cove because it was secluded from humans. It was meant to keep them safe, to prepare for our mating season. We don't know how it was found."

Mating season. A time where mers find mates and when mates prepare to have children. "Do you...?"

Mina frowns. "No, he was taken right before. Hanta and I were gathering food for the season to start. We never thought...I...I asked him if the humans tried to mate him but he said no. They didn't realize the time of year."

Kirishima relaxes. Their stupidity is probably what-

-saved Katsuki. "I wish I found him sooner."

"I'm just happy you found him." From where they are, they can just see Denki and Katsuki curled together. "We've missed him so much."

They're quiet for a little bit, just watching the two curled up on the sandy bottom of the floor. "Katsuki doesn't like humans," Mina eventually says. "They've hurt Denki a lot and all of us...well we've each lost someone to their nets. Katsuki was only a guppy when his parents-

-were taken from him."

Kirishima can't help but feel ashamed. Yeah, he may not have been the one who hurt them but he's a human. He's part of the group that causes so many deaths in their communities.

"But," Mina says, "he likes you."

Kirishima's head snaps up to look at her. He wasn't sure how Katsuki felt about him. Most of his actions seem to be more tolerant than anything else.

"He would have let Hanta maul you if he didn't. Katsuki's smart, he knows what your doing, understands what each-

-injection is. All he'd have to do is direct us to give it to him, but he chose to save you."

Kirishima gulps as he remembers the murderous look on Hanta's face. There's no doubt in his mind that he would have died a very painful death had Katsuki not stepped in.

Suddenly the words "not him" take on another meaning.

Both Katsuki and Denki break the surface. Katsuki swims closer to the platform and flicks water at Kirishima with his tail. "Hey!"

Katsuki clicks at him.

Mina laughs. "He wants to know if you have to leave again."

Kirishima wipes the water from his face. "No. I did everything I needed today."

There's a smirk on Katsuki's face and he looks at Denki. The two smile at each other and suddenly they're shooting forward, each grabbing one of Kirishima's legs and yanking him into the water.

The water is cool against his skin as he's submerged. He kicks his way to the surface and shakes his head. "Katsuki!"

Mina snorts as Denki and Katsuki lazily circle the human. "They want you to swim with them."

"I-I may not be able to keep up."

Katsuki swims up to him and boops his nose against Kirishima's cheek. Then he dives below the water and circles the human once more before swimming further away, clearly trying to initiate play.

"He doesn't care. Come on, human, Katsuki's hardly ever this playful."

Something about that knowledge has Kirishima softening. That coupled with his captivity means it's been a long time since he's even been able to play.

So, Kirishima takes a deep breath and dives after the two mers.

Humans swim an average of 2 miles per hour. Mers are.../much/ faster than that. It's dizzying really but clearly, these two go much slower than normal.

Both Denki and Katsuki allow Kirishima to catch them multiple times during their play. Each time he does, one of them will-

-press their noses against his cheek as if to say "good job".

When he finds himself caught in Katsuki's arms, Kirishima follows their example and boops his nose against the mer's cheek. A bright blush covers the blond's face and Denki swims around excitedly.

Something tells Kirishima that the action means something very significant to the mers. Whatever it is, Kirishima thinks it's a good thing.

When Denki clicks excitedly to Katsuki, the mer turns even redder and he hides his face in Kirishima's chest.

he's not really sure what makes him do it, but Kirishima leans over and boops Denki's cheeks as well.

The eel-like mer gives a squicking click and turns almost as red as Kirishima's hair. Katsuki clicks happily and rests his head against the human's shoulder.

Kirishima looks over at Mina. The alpha is smiling brightly at him, her look fond as she watches over them. "Uh...what just happened?"

"Something very /very/ good," she says but doesn't elaborate.

Katsuki clicking changes into a methodical trill. The sound being joined by Denki's own trilling notes.

Suddenly, Kirishima finds his arms full of two very happy omega mers. Their trilling clicks creating a calming symphony as they float together.

Kirishima's not sure how long they float together. The two mers continue their singing and it's just so comfortable. Mina remains on the platform watching the three of them in the pool. He doesn't know why she doesn't join them but she doesn't seem upset. In fact, she seems-

-content, almost happy, as she watches them.

Both mers have their weight resting fully on Kirishima but it doesn't feel like a lot. In fact, it feels really good holding them close like this. Maybe it's because the water helps him but he doesn't care. He just wants to-

-keep floating with both of them. In his mind, he can't help but picture them out in the sea, the sun shining down on them. He can just picture Katsuki's tail sparkling in the sun and Denki's sunkissed skin bathed in light.

The fantasy is so vivid that he's disappointed when-

-he feels hands on him, gently removing the now sleepy omegas. Hanta smiles toothily at him and pulls Denki into his arms. The alpha's long tail nearly circles all three of them.

Denki smiles dopily at him and nuzzles his nose against the alpha's, happy clicks sounding in his-

-throat. Hanta smiles back and points to where Mina is, a huge pile of fish and crustaceans on the platform next to her. The eel-mer lazily swims over and Mina passes him a wiggling crab.

Katsuki lifts his head and looks down at the human holding him close. He clicks-

-softly, before booping his nose against Kirishima's before swimming to Hanta and doing the same nose nuzzle thing.

"Hey, human," Mina says. "Katsuki says you have something that makes fish taste like it zaps you?"

He can't help but laugh at that. "Spicy mustard." It's kind of concerning how much Katsuki likes the stuff.

Hanta follows him to the edge of the platform. Denki holds out a bit of seaweed to the alpha and he smiles as he eats it directly from the omegas hand.

All four of them seem so comfortable around Kirishima. It's kind of mind-boggling, really, how much they trust him to be so open around him.

Kirishima doesn't want to think about when they eventually have to leave.