The collection of stories begins with Choice of Fate!, where Haruka Nanase, accompanied by his close friend Makoto Tachibana, begins the process of searching for a suitable apartment in Tokyo as he prepares for the transition into college life. During this search, they receive assistance from Kisumi Shigino, whose uncle happens to own a rental agency. Kisumi helps the duo secure a lease for an apartment situated conveniently close to a swimming pool. While visiting the potential residence, Haruka and Makoto encounter a young boy named Misaki Kuramoto, a budding swimmer who had previously been coached by the apartment's former tenant, Nao Serizawa.
The narrative continues with Cooling Down at a Secluded Hot Spring!, which focuses on Aiichiro Nitori as he struggles to decide on the perfect graduation gift for Rin Matsuoka and Sosuke Yamazaki. Meanwhile, Momotaro Mikoshiba manages to win tickets to the Anago Hot Springs. In a display of creativity, Momotaro and Aiichiro present these tickets to Rin and Sosuke through a complex and elaborate scavenger hunt. Once at the hot springs, the trip takes a comedic turn when Momotaro finds himself locked in a fierce competition with the captain of the Sofukan High School swim team over a specific capybara plush toy. Amidst the leisure, Natsuya Kirishima, an alumnus of Sofukan High School acting as a chaperone for the training camp, provides some poignant and wise guidance to Sosuke regarding his shoulder injury. As the trip concludes, Aiichiro and Momotaro give Rin and Sosuke traditional good luck charms as parting gifts.
In the segment titled Butterfly of Promise!, the focus shifts to Rei Ryugazaki, Nagisa Hazuki, and Gou Matsuoka, who are working together to produce a recruitment video to attract new members to the swimming team for the next school year. During the filming process, Gou discovers an outdated recruitment manual left behind by former club members. Inside, she finds a strategy referred to as "PKH East", which the group believes to be a highly resourceful technique for their video. However, their investigation reveals a humorous truth: "PKH East" was actually the nickname for "Perfect Kinniku (Muscles) Handsome Azuma", a former member whose striking physical appearance was the primary reason many female students joined the team. Although they are initially disappointed by this discovery, the experience ultimately inspires Rei to finish the recruitment video. During their investigation, Asahi Shiina also makes a brief appearance.
The final story, Eternal Blue of Setting Off!, centers around the members of Iwatobi High School and Samezuka Academy as they secretly organize a surprise going-away party for Rin, who is preparing to depart for Australia. The plans are complicated when Rin spots Gou and Momotaro together and mistakenly assumes the two are in a romantic relationship. His anxiety increases when he discovers that Momotaro intends to challenge him to a relay race alongside his older brother, Seijuro Mikoshiba. Fearing he might lose Gou's affection, Rin turns to Haruka for help, only for Haruka to reveal that Momotaro's true motivation was simply wanting a toy that Rin had acquired from a burger restaurant. Despite the misunderstanding, the competition proceeds, and the two teams face off in a race against the Mikoshiba brothers. Following their victory in the relay, the swim clubs gather to celebrate Rin's departure. Simultaneously, Ikuya Kirishima and Hiyori Tono are shown preparing themselves for the upcoming time trials at their college.
Following the conclusion of the stories, a post-credits scene appears with a cryptic message:
> "See you next stage"
This message served as an official teaser for the third season of the series, titled Dive to the Future.
