Free!-Timeless Medley- the Promise

Free!-Timeless Medley- the Promise (劇場版 Free!-Timeless Medley- 約束 Gekijou-ban Free!-Timeless Medley- Yakusoku) is the second and final film in the Timeless Medley film duology. It focuses on the Samezuka Swimming Club and its members, most notably Rin Matsuoka and Sosuke Yamazaki.

Plot
Sosuke Yamazaki, Rin's best friend from childhood, transfers into his class at Samezuka Academy. Rin and Sosuke had promised each other as children to continue their swim careers together, but unbeknownst to Rin, Sosuke has incurred a serious shoulder injury from overuse, yet continues to swim as they prepare for upcoming tournaments. While Rin is serious about swimming, Sosuke struggles to find a reason to continue, further straining their friendship.

At the regional tournament, Rin finally learns about Sosuke's injury. Sosuke, now cherishing the bonds he has forged with the swim team, is determined to participate in the team medley one last time. The team places second in the race, thus qualifying for nationals, and Sosuke decides to get medical treatment for his injury. Despite dropping out of the nationals, he offers to help Aiichiro Nitori and Momotaro Mikoshiba prepare.

In a post-credits scene, Sosuke warns Rin about Ikuya Kirishima, whose freestyle resembles Haruka's in both form and speed. Meanwhile, Ikuya refuses to attend the nationals' awards ceremony to call his brother, Natsuya Kirishima. Gou Matsuoka becomes determined to recruit new members for the next school year. Aiichiro, Momotaro, Nagisa Hazuki, and Rei Ryugazaki reaffirm their rivalry and plan a joint practice together. While Asahi Shiina exchanges farewells with his swim team at Kazami High School, he receives a text message from Kisumi Shigino. Haruka Nanase and Makoto Tachibana arrive in Tokyo.