Yuriko is taken in by the Yamakawa family—consisting of the parents, the eldest son Jun, and the eldest daughter Rumi—after a series of tragic misfortunes. Yuriko’s father vanished while trying to raise money to pay off a debt, and her mother tragically died in a car accident caused by sheer exhaustion and distress. Left entirely alone, Yuriko is rescued from an orphanage by the Yamakawa family, because her late mother and Rumi's mother happened to be high school classmates. Yuriko is assigned to share a room with Rumi, but nighttime brings a chilling visitor. A massive snake, measuring well over a meter long, slithers up the rain gutter and crawls across the roof toward their bedroom window...