Four boys named Haruka, Makoto, Nagisa and Rin all participated in a swimming tournament shortly before graduating elementary school and later parted ways. Years later, they reunite when Rin challenges Haruka to a race and wins. Not wanting to be defeated so easily, Haruka gathers Makoto and Nagisa and a new recruit named Rei to form the Iwatobi High School Swimming Club.
The boys of summer are back. Haru, Makoto, Nagisa, Rei, and Rin are reunited and the competition is about to get fierce. After the last swimming meet, the bonds of friendship have only gotten stronger, and with each passing day the boys continue to grow. This summer brings new rivals and new challenges.
Tōko Fukami's family runs a glass-working business in a small seaside town. She hangs out with her four best friends at a cafe called "Kazemichi." During the summer break of their senior year in high school, they meet a transfer student named Kakeru Okikura, who claims that a voice from the future talks to him, and that it's led him to Tōko. His arrival sets off a series of events that will make their final summer together one full of hope and heartache.
A girl named Mitsuki Kanzaki lives with her step-brother Yuya after her mother remarries. One day, Mitsuki is possessed by the self-proclaimed spirit of a young girl, Hiyori Kotobuki. Hiyori (in Mitsuki's body) must fall in love with Yuya to move toward the "Gates of Heaven."
Despite Ryuji Takasu's gentle personality, his eyes make him look like an intimidating delinquent. Class rearrangements on his second high school year put him together with his best friend, Yusaku Kitamura, and his hidden crush, Minori Kushieda. Along with these two comes Kushieda's best friend, Taiga Aisaka. Her delicate appearance contrasts with her brutal personality. Secretly in love with Kitamura, Taiga agrees to help Ryuji with his love interest as long as he helps her get closer to hers.
Haruka Kasugano and his twin sister Sora have lost both their parents in an accident, and with them all their support. They decide to move out of the city to the rural town where they once spent summers with their late grandfather. At first everything seems familiar and peaceful, but changes come as Haruka starts to remember things from his youth.