Souta Takatsuki and Rikka Amanome have been close like siblings since childhood, but Souta harbors deeper romantic feelings for her. In anticipation of her upcoming birthday, Souta searches for the perfect gift and discovers a mysterious book in a shop. The shopkeeper offers it to Souta for free, promising payment at a later time. However, Souta could never have predicted the intense desire the book would awaken in Rikka. As the true cost of the gift becomes apparent, Souta realizes it may be more than he bargained for.
