My seventeenth summer, three months before I went into isolation. The first daughter of Marquis Renarty, the girl who was called my "sister" had returned. Everyone in the mansion loved only her, but I didn't care. However Sometimes, the self-proclaimed lesser spirit I occasionally meet tells unexpected stories, and the woman called my "sister" tries to protect me, while the Duke I contracted with in a mutual agreement claims to be at a loss. And it seems that my affectionate childhood friend and I no longer have a simple friendship.