Nagisa, Rei, and the rest of the Iwatobi Swim Club have come to cheer on their former teammates at the All-Japan Invitational. Makoto tells them the story of how ever since Haruka swam for the first time, he'd been swimming only freestyle.
Makoto meets up with the members of the Iwatobi Swim Club who are in Tokyo for the nationals. Meanwhile, Haru continues his training.
Makoto has been unable to get in touch with Haruka following the friendly race at his training camp, making him worry that Haruka is dwelling on what happened. Then Nao approaches Makoto to tell him about a rumor he heard.
Haruka's next race is the All-Japan Invitational, which determines who will represent Japan at the global level. To prepare for this important tournament, Haruka is invited to a special training camp.
After the breakup of his middle school swim team, Ikuya decided to get stronger on his own and not rely on anyone. But Haruka, breaking out of his freestyle comfort zone to swim in the individual medley, tells Ikuya that he's not alone.
Hiyori still remembers the first time he saw Ikuya smile. Both boys grew stronger through rigorous training while they studied abroad in America... but seeing Haruka threw Ikuya off his stride. Now Hiyori wishes Ikuya would just forget about Haruka for good.
Haru, Makoto, and Asahi visit Shimogami University in hopes of talking to Ikuya, but even after looking all over campus, they can't find him. Hiyori, however, notices them and makes it his mission to keep them from seeing Ikuya.
Rin, now living in Australia, trains hard every day with swimmers from all around the world. Then a Japanese guy shows up where his team is training, challenging each of his teammates to races and beating them one by one. Even Rin is surprised when this newcomer reveals his identity...
The story revolves around Haruka Nanase, a boy who has always loved to be immersed in water, and to swim in it. Before graduating from elementary school, he participated in a swimming tournament along with his fellow swimming club members, Makoto Tachibana, Nagisa Hazuki, and Rin Matsuoka. After achieving victory, each of the boys went their separate ways. Time passed, and in the middle of their uneventful high school lives Rin appears and challenges Haruka to a match, showing Haruka his overwhelming power. Not wanting it to end like this, Haruka, gathers together Makoto and Nagisa once again and brings a new member named Rei Ryugazaki to create the Iwatobi High School Swimming Club in order to defeat Rin.