Story Summary: In which Rin is slowly coming to terms that mer-creatures exist, Haru is saved, Rei freaks out and Sousuke continually pranks his best friend (soon to be ex-best friend now). Inspired by sakura-rose12's Mer!Haru-Police!Rin AU on tumblr.

Chapter Summary: A tip off changes Rin's life more than he expects it to.

Note: Cross-posted from Ao3. So... uh, this is the long-promised AU based off sakura-rose12's idea on tumblr. I posted a snippet of it back in... what, September? (Yeah if you guys can spot it here it's really obvious I barely made any improvement on the story haha oh shoots)

Updates are really spontaneous as this is only a Universe for me to play around with, which means that I have no solid plot for it except for the first parts on her tumblr :) It also means that I accept prompts via my tumblr ask box! Feel free to fangirl about sakura-rose12's awesome AU (or just bounce off new ideas), we don't bite :D

I have no talent for titles or summaries. Feel free to suggest some via my tumblr ask box too :)

(It's xshiroichan by the way. My tumblr, I mean.)

*All chapters have not been revised nor beta'd unless explicitly stated.

Disclaimer: This is a non-profit document. Free! and Free! Eternal Summer belong to Kyoto Animation. High Speed! and High Speed!2 are works of Kouji Ooji.

Matsuoka Rin is having a shitty day.

No, wait, that may actually be the understatement of the century – and he was not being a drama queen, no matter what Sousuke says, thankyouverymuch – so he'd have to correct that.

Matsuoka Rin was having a very, very, shitty day.

First, he woke up late – because he swore Sousuke did something to his alarm clock, again. He didn't care if the other kept on insisting that he didn't do it because Rin knew he did do something – and subsequently got caught in the mother-of-all-jams that landed his ass even later for work.

When he got to the station – which was, by the way, ten minutes ago – his best friend – no longer if the other kept on pulling pranks like that – had strode up to him, tapped his head with the file he had been holding in his hand – Rin cursed the fact that the other was a full head taller than him so he could never return that gesture without embarrassing himself – and told him that they had a breakthrough.

An anonymous, urgent, tip off on a case they had been working on for months. And their higher ups needed a raid to be organized straight away.

While Rin would have cheered under usual circumstances in lieu of all the efforts he and his teammates had placed in their case, his situation made it difficult to be truly joyous about the "sudden gift-from-heaven" (as Sousuke had dubbed it). After all, who would be happy if they had to rush to their workplace only to find out that they have to rush again to somewhere else? (Plus, Rin wasn't exactly ready since he had to rush from his house down to the station.)

"These are the perks of being a policeman," Sousuke offered cheerfully, beaming at Rin who glared at him for being so upbeat. The redhead scoffed at his best friend's typical response to his grumpiness, closing the car door and fixed his cap.

"Just, go." Sousuke gave a knowing twitch of lips at the typical angry-and-pouty-Rin behavior and did exactly so.

The case Rin and Sousuke's team were working on was an extremely sensitive one, on an organization that dealt with illegal drug experiments that enhanced human capabilities. Rin had been skeptical at such a claim at first, but according to the people they've apprehended so far – all small-fries, they were never able to offer anything highly vital – the experiments were apparently highly successful and the organization was making huge amounts of money from the illegal drug sales.

The police raids on all known illegal drug sales and auctions had turned up empty for their particular organization. Rin frowned, the case had been cold and at a standstill for months, what were the chances of this certain anonymous tip off – which claimed the hold the information of the venue of those illegal experimentations – actually leading them right to the prize they seek?

Not very high, he concluded, feeling bored at staring at the scenery passing by. He wasn't going to get his hopes high just because of a seemingly accurate tip off.

Or this could simply be a trap. He silently told that part of himself to shut up.

He was jerked out of his trance when he felt the police car stop, and Sousuke gave him a look before exiting the car. Rin sighed, might as well get this over with, and exited the car.

The tip off had led them to an abandoned warehouse – because it just has to be an abandoned warehouse, how cliché – in a desolated area of the Yokohama port. He frowned, the old area, while no longer actively used, was still relatively close to the active trading areas by the bay. It's impossible for illegal experimentations to be carried out here. A look at the similar frown marring Sousuke's face clued Rin that his best pal had the same idea.

"Not the best place to hide, isn't it." He offered up tentatively, Sousuke turned and smirked in agreement, but it was another voice that answered.

"Probably because no one would think of looking for a lab in such a populated area, perhaps?" Nagasaki Yoshimi, another member of their team offered in her soft but steady voice.

That explanation had its merits as well, Rin conceded silently, and finally decided to speak up – for he thinks he's tortured his teammates enough as they all knew he was having a bad day and Sousuke's the only person who was brave enough to face him when he was all silent and broody (not to mention explosive all of a sudden).

"Well, let's see for ourselves, shall we?"

"Police! Freeze!" Sousuke's loud voice echoed through the large warehouse as he barged through the large metal – they had to detonate a small part of it –doors, the other members and Rin following his lead. Rin winced at the smell of chemicals that assaulted his nostrils almost immediately.

Well, looks like his day is finally picking up. That tip off was correct after all.

He could only describe the following events as downright chaotic. The scientists had looked at them and for a split-second everything was frozen, before the researches dropped whatever they were holding (some held on to the documents and Rin could only deduce that they were important) and ran towards the other side of the warehouse where he knew another smaller entrance existed.

It was too bad for them that they had police force members guarding that exit too.

Therefore, a huge number of researchers were apprehended within minutes of the raid. So despite there being one or two who got away, Rin's day was definitely picking up.

"I'm going to go check the back." He called out to Sousuke, who nodded as an indication of acknowledgement as he held down one of the particularly stubborn scientists who kept on fidgeting. Rin thought the guy was in for an especially rough treatment if he made Sousuke angry, and he wondered for a split-second if he should pity the poor fellow because Sousuke's got this feral look in his eyes that didn't bode well for anyone on the receiving end.

He navigated through weird machineries that created odd buzzes constantly, tables and shelves filled with beakers with oddly-coloured and smelling solutions, and even life-sized figures of the human body, the organs proudly displayed for all eyes to see. Rin winced, he hadn't seen those since high school when he took biology.

There was a light. And clanking sounds.

Rin blinked, looking towards the source and found a door leading to another – from the looks of it – smaller room. Placing a cautious hand on his gun, he tiptoed carefully towards the door, before peeking in.

That is bloody hell not possible! was Rin's first thought as he saw just what exactly was in the room.

Because there was no way mer-creatures existed. Nuh uh. Nope. This isn't The Little Mermaid (the wonders of having a younger sister), no. Just. No.

Apparently they do, though, and Rin was left staring in stupefied wonder at the half-human with a shiny blue fish tail trapped in a huge tank. He was glad that he didn't drop his gun in shock because it was only when he saw the creature – what was he supposed to call him?! – glaring fervently at something then he registered that there was another scientist in the room.

"Freeze!" The other human jumped in surprise and turned back at him, grimacing at the gun pointed at him. Rin got a good look at the other, his red spectacles slanted on his nose and usually-tamed hair mussed up.

"Wa – wait! Don't shoot! I was just trying to save him!" The other waved his hands frantically, gesturing to the creature in the tank. Rin frowned, before realizing that the merman – it seems like his mind had finally submitted to the idea of mer-people existing – was staring at them with an almost-morbidly curious manner.

Not lowering his gun, he snapped at the scientist. "Explain yourself."

"Lo-look, this poor thing here was experimented on by some of my… co-workers. He's been treated really badly around here during the tests that they conducted on him! I'm just trying to bring him away because god knows that if the government gets their hands on him they'd do the same thing! You have to help me!" The scientist insisted, and Rin's frown deepened.

He had a point, but according to protocol, anything from the labs was to be submitted as evidence and obviously, the merman is a crucial piece of important evidence against the organization, Rin was trained – drilled, really – in the academy to follow the protocols like the gospel.

But was he cruel enough to leave the creature at the mercy of the government? Obviously the merman was a… biologically unique creature, but he is still, ultimately, alive.

Rin doubted that he could ever be heartless enough to leave him to the government.

"How do I know that this isn't a trap?" He stared the scientist down, noting that the other, while on the verge of bursting into hysterics, was extremely desperate. His eyes told Rin all he needed to know, but he needed verbal confirmation.

"Damn it! You can arrest me now but you have to promise me that no harm will come to him! It's not like I enjoyed watching them experiment on him! You have to trust me, please!" Rin was amazed at the pitch that the other's voice had risen to, before sighing and returning his gun to its holster after clicking the safety back on. The other didn't seem to be lying, and Rin prided himself on being a good at detecting lies when the situation calls for it.

He looked at the scientist with a blazing, determined, red gaze.

"I'll help."

The other lit up like a child on Christmas, "Thank you! Thank you so much!"

Rin was getting uncomfortable with that, he sighed and grumbled, "So how do I get him out?"

The other looked thoughtful. "I can't take him with me since I don't have any means of transporting him… Could you bring him to somewhere safe, first?"

"What?!" How the heck was he supposed to do that? The merman had a freaking tail, despite looking perfectly human on the upper body, goddamnit.

"Don't look at me like that!" The scientist defended vehemently and turned towards one of the cupboard, rummaging through it and pulling out what looked like white cloths. Rin squinted at it, the dim light – other than the one shining onto the tank, could these people be any more obvious?! – making it difficult to see but he could make out the rough cutting of a shirt.

"Put this on him," the other – Rin really needed to ask for his name, it was getting tiring referring to him as "the other" or "the scientist" – shoved the white T-shirt at him and shrugged off his lab coat, and passed it to Rin as well.

"You could probably cover his tail with this."

Rin winced at the reminder, and looked up at the mer-creature, who was now regarding them with suspicion. He couldn't blame him really, the people here haven't been the kindest to the creature as far as Rin heard from the scientist.

"You know," he began after a short silence – in which the three of them regarded each other, the creature with wary eyes and the scientist with hopeful ones, "I should probably arrest you just for your participation in…. whatever this is." The other grimaced but looked oddly steady despite Rin's claims.

"It's fine if I get arrested, I probably deserve it anyway for working for them." He spat out, turning to look at the merman with a melancholic gaze. Rin raised an eyebrow, before clearing his throat at the other's outburst and continuing.

Sousuke's going to kill me for this.

"But I won't." The scientist's head snapped towards him so fast that Rin had to wonder why the other's neck hadn't snapped yet. His eyes were wide to inhumane proportions, though, as if he didn't expect to be spared by a policeman of all people, despite Rin's agreement to help him out.

Rin thought his expression looked kind of silly, especially with his glasses positioned crookedly, hanging from the bridge of his nose. He did give him credit for recovering quickly, though, as the other cleared his throat to rid himself the effects of his awkward outburst and pushed his glasses up.

"Why?" It was asked with a faint voice.

"Because," Rin paused, "Because I want answers." He knew he wasn't going to get them if this guy's thrown into the kind custody of the police. And he needed answers damn it.

The mer-creature was extremely curious, after all.

The other seemed to ponder over his reply, before nodding in understanding. Taking a deep breath, he sighed out.

"Ryugazaki Rei."

Rin blinked. "Huh?"

"That's my name. What's yours?"

"O – oh, Matsuoka Rin."

"Isn't that a girl's name?"

"Shut up, isn't yours?"

"Touché."

The splash of water brought the anxious mer-creature back to their attention. Ryugazaki gave Rin a look, and he sighed, before bracing himself and walking towards the tank.

He hadn't a single idea on how to approach a frightened merman – because those scenarios were not covered in his training, obviously – but he hoped the other had relaxed enough for Rin to approach him.

The mer-creature watched him cautiously as he approached the tank with as much finesse as he could – he silently cursed himself for not paying attention to those compulsory courses on how to approach traumatised victims of crimes because that would be ultra useful right about now – but that had always been Sousuke's job between the two of them, so Rin was not very good at it.

Evidently, seeing as the creature kept on moving backwards, as far away from the approaching Rin as it is possible physically. The redhead grimaced when the tank shook as the creature collided with the other side of it. Taking a deep breath, he slowly reached into the tank and was surprised when the creature began to swim towards him –

Rin winced when the mer-creature bit him, but was determined to keep the hiss that escaped his mouth to minimum so as to not scare the other away. He heard the scientist – Ryugazaki – gasp in the background.

Good thing he had a high pain tolerance.

Trying desperately to turn his crunched-up expression into a soothing smile, he reached for the other's head with his other hand, running through the damp tendrils of smooth, dark tresses, trying to convey how he didn't want to harm the other. He saw the other's eyes widen and the creature relish his bite on Rin's injured hand, the blood flowing out at a faster rate and staining the water red. It seems like he had understood Rin's message.

"Your hand!" He mentally sighed at the scientist's overly dramatic antics. It seemed to be part of his nature, Rin mused, and it would've been entertaining if it wasn't the fact that he had a mer-creature to save.

"Don't worry, it only looks bad." He replied, reaching for the towel that was hanging on Ryugazaki's arms. "Gimme that."

The other creature was still regarding Rin warily – to a lesser extent, however – when he reached into the water to bring the other up. He tensed when Rin wrapped the towel around his tail.

"Don't worry, this is so that no one will see it." He murmured in a – what he hoped was – comforting manner and he smiled when the other relaxed, still regarding him with those bright blue eyes – now that the suspicion was completely gone, the blue irises shone with brimming curiosity directed towards Rin.

The redhead turned towards Ryugazaki, who was looking worriedly at the creature in his arms. The scientist's hands were clenched into tight fists at his sides. Rin frowned.

"You should get out of here quick. There should be lesser people by the back entrance. Meet me at the Starbucks down at the fifth Minato-machi tomorrow at noon." Rin shot him a look, "and I will report you and turn you in if you don't show up." Ryugazaki huffed, giving him a glare that said 'do you really take me as someone that shallow' before turning to escape the warehouse.

Rin watched him go, and looked down at the merman in his arms – he was still staring at him – before sighing.

He'd have to sneak him back into the car, and that's still not the most difficult part.

Avoiding Sousuke was.

Rin winced.

Notes: My favourite so far is Sousuke (wha-?!) yup. HAHA. I have yet to watch ES so it's kinda hard to get his character right. I hope I did.