Rin Matsuoka is the main antagonist of the first season. He's a rival to Haru and is his opposite in many ways. Though, his hot-headed and competitive spirit seems to be the most obvious contrasting feature. He takes swimming very seriously and aims to become a competitive swimmer in the future. If he has to go through his childhood friends to achieve that dream, he's willing to do that.

Rin's voice is mid to mid-low. It's powerful, his emotion speaks volumes every time he speaks, as he's very passionate about what he believes in. He's not strong all the time, though. He does break down and has his vulnerable moments, so do keep this in mind.