Hinako lives alone by the sea, quietly drifting through life after losing her family years ago. One day, a mermaid named Shiori saves her from a monster and says she’s come to eat her—just not yet. Until then, Shiori will stay by her side and keep her safe. In that moment, a deep hope swells in Hinako: Maybe this girl can finally grant her the ending she’s been waiting for.

In a seemingly ordinary rural town, something strange is happening to the residents. But Shizuru Chikura is more concerned for her missing friend. Determined to find her, Shizuru and three other girls board an abandoned train and travel to the outside world, unsure if they'll make it back alive. As they venture toward the unknown, the question looms: What awaits them at the final stop?