Rin Matsuoka

In the first season of the anime, he is a second-year student at Samezuka Academy, a third-year student in the second season, and a university student in the third season. He refers to himself as "ore." He is 177 cm tall, weighs 68 kg, and was born on February 2nd under the sign of Aquarius. His best subjects are English and Math, while his weakest subjects are Japanese and Classical Literature. His favorite foods are meat, kimchi, and spicy foods, and he dislikes sweet foods. His hobbies include muscle training, working out, and running while listening to music. He is characterized by his jagged, shark-like teeth. He is a rival to Haruka and has a habit of pulling the rubber band of his goggles or cap from behind.

He transferred to the school where Haruka and the others were in the sixth grade and later met them at a swimming club, becoming friends. He aims to become an Olympic athlete and decided to study swimming in Australia before entering middle school. Just before leaving Japan, he invited Haruka, who was only interested in freestyle, to participate in a relay race, promising to show him a new world.

He returned to Japan a month before the start of the first season and transferred to the all-boarding Samezuka Academy, starting dorm life. While he was bright and sociable as a child, by the time he reunited with Haruka and the others in his second year of high school, his attitude had become more abrasive, confusing Haruka and the others, as well as Gou. At the time of his race against Haruka at the Samezuka Academy pool in the second episode of the first season, he was not yet a member of the swimming club. After learning from Makoto that Haruka and the others had formed a swimming club at Iwatobi High School, he decided to join the swimming club.

His father also aimed to become an Olympic swimmer as a child but couldn't achieve it and became a fisherman. He died in a drowning accident when Rin and Gou were young. Rin harbored a desire to fulfill his father's dream. However, he hit a wall while studying abroad and suffered so much that he wanted to quit swimming.

His events are freestyle and butterfly, and despite having excellent records, he was fixated on competing against Haruka, entering only the freestyle event at the prefectural tournament in his second year. However, he realized that he didn't just want to beat Haruka but wanted to swim with him and the others again. By swimming a relay with Haruka and the others once more, he freed himself from past constraints and began to pursue the Olympics as his own dream rather than his father's.

He then regained his original personality and was appointed as the new captain by Mikoshiba, who retired from the club. He worked hard towards his goals for the sake of his friends and his dream. Due to his performance at the prefectural and regional tournaments in his third year, he received many scouting offers from universities. However, he received an invitation from his mentor in Australia and decided to join his mentor's team after graduation, heading to Australia.