Kurotsuta Yashiki No Himegoto

Kurotsuta Yashiki No Himegoto summary:

When she was little, Chizuru lived in the house where her mother worked as a housekeeper and played all day with Yukihiko, the little lord of the Black Ivy Mansion. At some point she had to leave, and when she returns some years later she meets Yukihiko again. He invites her back into his house. But the mansion hides a terrible secret that Chizuru doesn't know…