Set in the distant future, Kagami Village is a suburban mountain settlement that has been left behind by the advanced science and technology of urban centers. "If you're not well behaved, a look-alike will come." Higure Akane, a middle school student residing in this village where an old legend persists, was anticipating a reunion with her older sister, Higure Sui, who had just been released from the hospital after a year. However, shortly after her sister's discharge, Akane receives a phone call stating, "The person in that house is not your older sister."