Ep. 1: Akane Higure questions her sister's identity after a mysterious phone call in Kagami Village.

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Set in the remote Kagami Village, an area neglected by urban technological advancement, old folklore warns of a creature called a Double. Akane Higure, a middle school student residing there, anticipates the return of her older sister, Sui Higure, who is finally discharged from the hospital after a year. However, shortly after Sui arrives home, Akane receives a single phone call. The caller informs her that the girl currently at home with her is not actually her sister. This revelation disrupts Akane's expectations and introduces the lingering threat of the Double mentioned in local legends, casting doubt on the identity of her returned sibling within the isolated mountain community.