In the final summer before high school graduation, Kyohei Kashiro is adrift. A former swim star, he left his college application and career plan form blank, unable to decide between staying local or moving to the big city, between continuing to swim or quitting altogether. The biggest question, though, is not about his future—it is about his best friend Eiji Honda. Ever since their first day of high school, they have been inseparable. But now Eiji has confessed his love. Kyohei panics, convinced their friendship will end. Yet once he starts paying attention, he notices a side of Eiji he had never seen before: a shy, unexpectedly cute boy who has secretly adored him for years. Swept up by the moment and by his own fluttering heart, Kyohei agrees to start dating.

Their new romance unfolds across the carefree days of summer. Every day becomes more exciting now that a best friend is also a lover. Together they navigate the small hurdles of a first relationship—learning to read each other’s moods, sharing affectionate moments, and figuring out how to be a couple while still being the same two people. But the looming future does not disappear. Eiji also wrestles with uncertainty: he wonders if he has ruined their friendship or if Kyohei truly loves him back. As the season draws to a close, both boys must confront what they want for themselves and for each other, discovering that change, though scary, can also be magical. Their last summer together becomes a spark that lights the way into adulthood.