2011, Seta Souji moves to the countryside to his uncle's house due to his parents working abroad. Not very friendly, he however manage to make a few friends there, and they all decide to solve the mystery behind the sudden cases of serial murders that strikes the area.
Kazumi thought he was good friends with a boy he had known for ten years, Rihito. One day, while they were out in town together looking for a shop selling masks for their school's masquerade ball, Rihito suddenly disappears. Kazumi drops out of school and starts looking for him, and will soon set foot in a totally new world.