High☆Speed! 

Nanase Haruka is a sixth-grade elementary school student who loves connecting with the water and feeling the water as he swims, and he attends a local swim club together with his childhood best friend Tachibana Makoto and Hazuki Nagisa, one year younger than the both of them. Then, one winter's day as graduation draws near, Matsuoka Rin transfers into Haruka and the others' school from another swim club. Through swimming, Haruka strengthens his bonds with Makoto and Nagisa, as well as with Rin; at which point Rin, with his passion for the medley relay, suggests they form a team together and enter a tournament...