“The girl at home with you… isn’t your sister”
In the distant future, on the outskirts left behind by the rapid concentration of advanced science and technology in urban areas, lies a remote mountain village known as Kagami Village. "Behave yourself, or a Double will come for you." Such old folklore still lingers in this village. Akane Higure, a middle school student living in Kagami Village, has been eagerly awaiting the return of her older sister, Sui Higure, who is finally being discharged from the hospital after a year. However, not long after her sister comes home, Akane receives a single phone call. "The girl at home with you… isn’t your sister."
