Matsuoka Rin

Rin is Haruka's rival and was his former teammate in elementary school. He comes back to Japan after studying abroad in Australia during middle school and becomes estranged to his former teammates due to a change in his personality, which came after he suffered a tough loss in a race against Haruka during their first year of middle school.

Despite his self-proclaimed rivalry against the members of the Iwatobi Swim Club, he continues to demonstrate concern for them, particularly for Haruka.