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Second year high schooler, Haruka Nanase, reminisces about the times spent with his friends in their grade school swimming club and of wanting nothing more than to be a freestyle swimmer.
In the present, Makoto Tachibana, Haruka's best friend, goes to pick him up for their second day of school at Iwatobi High. While having lunch that day, they encounter their old friend, and recent transfer, Nagisa Hazuki. Nagisa not only wishes to swim with Haruka like they used to, but also suggests that they dig up a time capsule containing a relay trophy they had won with their friend Rin Matsuoka at the dilapidated Swimming Club.
While there, Haruka once again reminisces over a photo of the race, being the last time the group had swam together before Rin had moved to Australia to enroll in a swimming school. Afterwards, the group shockingly runs into a completely changed Rin in the hallways. Rin immediately challenges Haruka to a race, until they discover that the old pool is empty.
At school the next day, a scarlet-haired girl observes the group with a friend and remarks of them being old acquaintances before Makoto and Nagisa are reprimanded by a teacher for trespassing at the swimming club. As Makoto and Nagisa visit Haruka that evening, they discover the scarlet-haired girl turns out to be Rin's sister, Gou Matsuoka attempting to pay Haruka a visit. They then learn from her that Rin is now attending Samezuka Academy upon his return from Australia.
Afterwards, Makoto and Nagisa convince a reluctant Haruka to visit Samezuka by tempting him to a swim duel in the school's pool. Upon arriving, they wait until the school's swimming team is done with practice and break into the academy's swimming pool. They are then discovered by Rin who aggressively orders them out. Haruka then steps out of the pool and challenges Rin to a freestyle match.