Free revolves around Harase Nanase, a boy who always likes to be immersed and swim in the water. Before finishing elementary school, he participated in a swim with his swimming club friends, Tachibana Makoto, Hazuki Nagisa, and Matsuoka Rin. After winning the prize, each of them chose a different path.
As time went on, amidst the peaceful days of high school life, Rin appeared and challenged Haruka, showing Haruka her overwhelming strength. Unwilling to end things like that, Haruka reunited with Makoto and Nagisa, along with a new member named Rei, to set up the Iwatobi High School Swim Club to defeat Rin. Haruka, Makoto, Nagisa, Rei, and Rin come together in a story about swimming, youth and friendship.