After spending their first year of high school in peace and quiet, Haruka and Makoto run into Nagisa, a new student who was a member at a swimming club with them when they were kids. That swimming club is being torn down, so the three of them sneak in to dig up a time capsule that they buried in the back, which is when they are reunited with Rin, the fourth member of their group who left to study abroad.

Makoto and Nagisa watch with their breaths held as Haruka and Rin engage in an intense race. However, they notice that Rin appears to be have changed. At the same time, Nagisa prepares to start up a swim club with help from Rin's sister Gou.

As prefecturals draw near, Haruka and the other swim club members continue to improve. Meanwhile, Rin reveals his motivations for swimming. The swimmers must now show what they have accomplished at the tournament.

The Iwatobi Swim Club must win to advance to nationals. As the tournament draws near, the members get nervous. Meanwhile, Rin grows increasingly irritated. As it comes time for the medley relay, each member must find their own answer as they step up to the start line

Haruka and his friends have grown after last summer’s tournament. Amidst the hustle and bustle of training for their individual events, their daily lives continue as usual. However, a new season now approaches!

The crew ponders how to attract new members to the Swim Club. Haruka is called in by Amakata-sensei to discuss his intended career path, but as always, Haruka moves to the beat of his own drum. Meanwhile, Coach Sasabe brings an interesting opportunity to the boys…

As the tournament continues, Sousuke finally tells Rin about how he’s passed their years of separation. Rin is concerned at Sousuke’s nonchalant attitude toward certain things and tries to speak his mind. Meanwhile, the Iwatobi Swim Club looks toward the relay final.

Having faced his feelings honestly at last, Haruka tells Makoto, Nagisa, and Rei what he has decided for himself and his future. The Iwatobi Swim Club is once again fully united as they mount the starting block at nationals, ready to swim for themselves, for their friends, and now, for the future as well.

Haruka has entered Hidaka University, where he's now training with the swim club to prepare for a newcomer tournament. One day, he runs into Asahi, a swim teammate from middle school. Haruka is later joined by Makoto, who also moved to Tokyo, at a coffee shop to catch up with Asahi... and the topic quickly turns to Ikuya, another teammate they swam with in middle school. On the day of the newcomer tournament, Haruka and Asahi are in the same race for the first time in years... and the spectacle is watched by Hiyori, who calls Haruka an "inferior copy of Ikuya." After the race, as Haruka is walking through the halls with Asahi, he catches sight of Ikuya passing by..

Haruka and his relay teammates decide to hold a training camp in the summer of their second year of middle school. During the night, Haruka heads out to the pool and finds Ikuya looking up at the stars.

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...

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.

The Iwatobi High School Swim Club is participating in a joint training camp with the Samezuka Academy and Soufuukan High School teams. Sousuke is also participating as an alumnus. In the midst of the excitement, Rei and Nagisa notice that something is odd about Romio's swimming. Then Shizuru tells them the story of what happened to Romio in middle school...

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.

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.