Ballad of an Evening Butterfly

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 clothes of black, he descends the long spiral staircase to the basement.
There sits a pure white maiden.Crimson eyes and white skin---a 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.
She is the "ChouTsuki," and Sera was invited to the mansion to be the ChouTsuki's "sacrifice."

[From Deja Vu]