Nanase Haruka is a sixth-grade elementary school student who is deeply passionate about swimming and connecting with water as he glides through it. Together with his childhood best friend Tachibana Makoto and Hazuki Nagisa, who is a year younger than them, he joins a swim club in their hometown. As graduation nears, they welcome a new transfer student, Matsuoka Rin from another swim club, on a wintry day. Haruka's bond with Makoto and Nagisa, as well as Rin, is strengthened by their shared love for swimming. Rin, who is particularly enthusiastic about medley relay, suggests they form a team and compete in a tournament.
