Twin sisters Mio and Mayu Amakura visit a stream they remember from their childhood memories. The area will soon be submerged by a dam. As Mio reminisces, her older sister Mayu is drawn away by a crimson-coloured butterfly, leading her toward the rumoured village that no longer appears on any map. It is a village of vengeful spirits hunting for the twins girls who fled their ritual. A village of never-ending night. As Mio tries to find Mayu and escape from the village, her actions unknowingly retrace the horrors of the past. In the deepest reaches of the village, Mio uncovers the truth behind the “forbidden ritual that must never be witnessed.”