Ringisa

Ringisa is the slash ship between Rin Matsuoka and Nagisa Hazuki from the Free! fandom.

High✩Speed!
When they first met, Nagisa introduced himself and asked Rin to check his swimming style; Rin reluctantly obligued and observed that it didn't look so much as a butterfly but rather as a "grasshopper style". Then, after giving a couple of absent-minded pointers (which elicited a few complaints from Nagisa for not being paid attention to). From then on, they develop some sort of teacher-student relationship, in which Rin observes Nagisa's swimming and gives hima few pointers on his technique.

One day Nagisa tells Rin that he wasnts to have a break from butterfly swimming so he could prepare himself for the upcoming timing for breastroke, he said he was really fast at said style and then he'd become the fourth member of the relay team that Rin was looking for. Rin is not convinced at first, but he agrees to the deal after seeing how Haruka agreed to becoming part of the relay team if Nagisa got first place, saying that it could work to his favour and that if he did win, then it proved he had what it took.

During one conversation in the locker rooms, Rin says that if they were to work together they should talk to each other in a first-name basis, and thus Tachibana would be "Makoto", Nanase would be "Haruka", and that Nagisa would still be "Nagisa". He then proclaimed that he should be called "leader", to which Nagisa complained that it would be "weird, after all" and "isn't 'Rinrin' better?". Rin said that that nickname was his trauma and tried to intimidate Nagisa into not using it, with little success.

During one practice, Rin notices Nagisa doing a "monster-like speed-gaining" stroke when he is against someone, he ended up being somewhat afraid of it, and dashed out of the pool. He wonders if it has something to do with his "wide, clear eyes" and the way they "seem to stare into your soul".

They tend to banter a lot, and both Haruka and Makoto seem to think their friendship is somewhat strange.

Free! - Iwatobi Swim Club
When they meet again, Nagisa seems excited to see him again and goes to greet him, but Rin does nothing to acknowledge him nor Makoto, instead choosing to challenge Haruka to a race.

Nagisa, like Makoto and Gou showed concern towards the changes that Rin had gone through after living in Australia and what might have caused it.

Fanon
A rare pair, Ringisa has a small following.

Fandom
AO3

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Trivia

 * Nagisa's spirit animal is a penguin meanwhile Rin's is a shark.
 * Nagisa's swimming stroke is breastroke, and Rin can swim all strokes but he focuses on butterfly and freestyle, thus being an individual medley swimmer.
 * It was mentioned in High✩Speed! 2 that Rin and Nagisa exchanged letters while the former was in Australia.
 * In the CD Track Rin And Nagisa's Day Off, they go to the arcade and won a stuffed toy called  "Mizushimashima-kun".
 * Nagisa tends to add the "-chan" suffix to everyone's names, regarldless of their gender. Moreover, he calls Rin "Rinrin".