The story is set in the distant mountain village of Okukozome-chou. Haruka Kazugano and his twin sister Sora have fond childhood memories of going to the village to visit their grandfather during their summer vacations. However, after losing their parents in an accident, the two must move in with their grandfather.
The twins get reacquainted with their old childhood friend Nao Yorihime, their new classmate Ryouhei Nakazato, the shrine maiden Akira Amatsume, and Akira’s friend Kazuha Migawa. All seems peaceful and familiar. However, beneath the surface is a secret promise that the twins made with each other long ago, the whereabouts of an important lost item, and the real reason they chose to come back here.