The shark is known as a vicious and relentless predator, capable of locking onto its prey with just the smallest hint of blood in the water, and while its movements seem as graceful and fluid as any regular creature that lives its life in the water, a shark doesn't live an overly idle life, nor does it believe in mercy. Fittingly enough, with his row of sharp shark-like teeth, Rin goes about his own life almost exactly like an actual shark's, having the same sort of determination and ferocity of a killer of the ocean... albeit he doesn't go around killing and eating people. Rin didn't always have this same sort of hot-blooded attitude, having been more of a cheerful and charismatic child when he was much younger, but he still had the same sort of drive to be the best and live his life to the fullest, unwilling to let any sort of boundaries get in his way of attaining the dream of becoming an Olympic swimmer, a dream that used to belong to his father until he gave it all up to become a family man, only to be killed by the very thing he loved; the ocean, having drowned in a fishing boat accident. The event was what sparked Rin's motivation to achieve what his father hadn't been able to have, and in order to take better advantage of his potential, he would eventually move across the seas and study in Australia, leaving behind a small group of his friends. But when he finally returned, he wasn't the easy-going and cheerful boy he used to be.

Rin has a firey spirit, one that allows him to focus on his desires and goals to an almost obsessive extent. He spends a lot of his free time reading books on how to better himself and practices his swimming techniques whenever he gets a chance, and he has high enough expectations of himself that not getting a fast enough time or screwing up a training session can put him in a very negative move. Dealing with losses are not part of his specialty, because what he expects from himself is the very best, and failure just clearly isn't an option. He'd gone to Australia in order to become a better swimmer and pave his way further toward being an Olympian, but the fact of the matter was that he had ended up in unfamiliar terrain, with no one to rely on and no one to support him but himself, and so because of this, Rin learned to become more reliant on his own skills and no one else's. He's intent on being the best on his own grounds and having no hesitancy when it comes to his swimming, as well as with other people, which means that new friendships are hard to hold onto and build. When Rin returned to Japan and enrolled in a new school and joined the swim team, he had no real attachments to anyone other than his swim captain, Mikoshiba, and one of his underclassmen who happened to be his roommate, named Nitori. Nitori idolizes him to an amazing extent, but Rin never bats a single eyelash over it or shows any real signs of feeling praised. At the most, Nitori seems like background noise to him, nothing he pays attention to or needs. They're just empty words, falling back upon the rest he's had in his life, including those of his old childhood friends.

Because of his focus on swimming, Rin doesn't ever find the time or the place to reconnect with the group of friends he'd had as a child; Makoto, Nagisa, and specifically of all, Haruka, whom could have easily been considered as Rin's best friend in the past. Rin cared for Haruka immensely and focused on him so much that he demanded he swim in a relay with him, but it wasn't until the two faced off in a race when Rin returned to Japan that resulted in Rin's loss that their friendship crumbled. Even as an adult, though he's not very adept at showing it, Rin holds a very high regard for the relationships he holds with people, but when conflict comes along, he becomes frustrated at his inability to communicate his emotions or handle the situation. Rin is all about action and not quite considering the consequences, so he'd much rather yell and shout then take a moment to think things through, or at the worst, break down into tears. During his entire time back in Japan, he never takes a chance to talk things out with Haruka and the others to see what sort of position their friendship is in, and the only reason they ever end up meeting up continuously is due to Haruka's group of friends forming a swimming club along with another student, named Rei. Haruka's group soon decides to train and prepare for a swimming competition, and soon his focus isn't just on the swimming but on meeting Rin, and when Rin finds out the news of their plans, his only intention is to beat Haru in another swimming match to prove himself as the better one.

Though he plays himself off as a cocky and head-strong individual, Rin has a surprisingly fragile weakpoint that brings him to pieces if it's touched upon. Rin has been very alone for a large portion of his life, mainly only having the companionship of his younger sister, Gou. Dealing with other people in an environment outside a swimming pool is downright difficult for him, and after fixating so heavily on the loss that Haruka had given him, all Rin could want upon returning to Japan was beating him and regaining his pride. But, even after finally winning a match against Haru, Rin realizes that it wasn't the answer he wanted, and that there was something else he needed to attain to feel complete again. It's when he loses his chance to swim against Haruka again that Rin realizes what he'd secretly been aiming for all his time in Japan; to be friends with Haruka once more and to not swim against him, but to swim with him. Deep down inside him, he knows that friendships are the things that forms a large portion of who he is as a person, and gives him the right determination to better himself and be true to himself. Isolating himself with his competitive nature only hurts him, because when it comes down to it, he's still that lively little boy that only wants to swim and have fun, but more importantly, have fun with the people he cares about.

On the outside and when his emotions and temper get the best of him, Rin is as unrelenting and vicious as a shark, but deep down, he's exactly how he used to be as a child, just a boy that wishes to find his own happiness, especially among those who help provide it for him. His sister Gou put it upon herself to create a swim team just for the sole fact of wanting to find a way to bring the young version of her brother back, wanting to see that happy grin he used to wear as a child, and when Haruka realizes that Rin's frustrations aren't just a sole factor of how inept he grows to become over his capabilities as a swimmer, Rin soon learns what it is that had been missing his whole life, the single thing he needs in order to be "free": friends. And friendships are the things that are so integral to a person that there's no need to prioritize competitions and pride over them, which is what Rin ultimately embraces. It's been a long and hard road for Rin to regain the old ideals that he's had as a child while still retaining his unrelenting ambition, but deep down, he takes on any challenge that meets him, and so learning to be a reliable friend again shouldn't prove to be difficult. Sharks aren't easily intimidated by much, and neither is Rin.