An unnamed math teacher at St. Lucia Academy is found dead in a pool. Staff at the academy are worried about the first witness to the scene, Mizuho Kousaka, as this is the second time Mizuho has been witness to a dead body. Out of curiosity regarding this fact, Shion Sonozaki approaches Mizuho and befriends her. Shion offers Mizuho "Shion's special amulet", a charm that Shion claims improves mood and can grant wishes. Hoewver, this charm is simply an eraser.