Ballad of an Evening Butterfly is a visual novel rated 15+ for mature themes. Having lost his memory, Sera Kaoru stops in the forest and visits a strange Western-style house. Guided by the house's owner, the boy in black clothes, Sera descends the long spiral staircase to the basement. There sits a pure white maiden, breathtakingly beautiful "girl". Sera's job is to distract her from her boredom. He reads a fairytale to her, and upon completing the peaceful job, the boy in black clothes informs him that "girl" is the "ChouTsuki", and Sera was invited to the mansion to be the ChouTsuki's "sacrifice".