Ep. 1: Ko Kitamura and Wakaba Tsukishima share a childhood bond that deepens through shared experiences and tragedy.

1

Ko Kitamura and Wakaba Tsukishima were born on the same day in the same hospital, leading Wakaba to treat him as her boyfriend. During summer vacation, Ko takes Wakaba to swimming lessons on his bicycle. To avoid Osamu Akaishi, who likes Wakaba, Ko joins a sandlot baseball game organized by Daiki Nakanishi. Despite never playing before, Ko hits a game-winning home run using skills practiced at the Tsukishima family's batting cages. After their joint 11th birthday, Wakaba gives Ko a schedule of birthday presents for him to give her through age 20. Shortly after, Wakaba drowns while saving a younger girl at an overnight swimming camp. Ko struggles with grief until he sees Akaishi weeping outside Wakaba's house, realizing he must cry. The credits show time passing until Ko and Wakaba's younger sister, Aoba Tsukishima, are in junior high school.