Mozumi Aruto lost his childhood memories long ago, along with any connection to the sound of the piano. His younger brother Tokio, by contrast, plays with natural brilliance — a talent Aruto watches from a distance with a quiet ache he cannot fully name. He has not even been able to confess to the classmate he loves. Then, in the final summer of high school, a girl he has never met appears before him and says she carries memories of the future. What follows is a bittersweet, fleeting story of love, loss, and the choices that cannot be undone.