Shouya Ishida starts bullying the new girl in class, Shouko Nishimiya, because she is deaf. But as the teasing continues, the rest of the class starts to turn on Shouya for his lack of compassion. When they leave elementary school, Shouko and Shouya do not speak to each other again... until an older, wiser Shouya, tormented by his past behaviour, decides he must see Shouko once more. He wants to atone for his sins, but is it already too late...?

The Iwatobi Swimming Club is back and struggles with the recruitment of new members. At the same time, senior members Haru and Makoto have to figure out what to do after high school, challenging their love for swimming. Meanwhile an old childhood friend of Rin returns and stirs up some trouble - especially with Haru. How is the Iwatobi gang going to respond?!