Every day is a normal day in the small town where Kasuga Arata lives. However, everything changed the day the Black Sun and a sorceress appeared before him. The Black Sun caused the Collapse Phenomenon that destroyed the city he lived in. Because of this, her normal life was artificially reconstructed by a Grimoire that her childhood friend had left her. After all, what was the purpose of the magician coming to town? What will he do with the gift of the Grimoire?