A wealthy man takes in two orphaned sisters, offering them a home. He appears kind at first, but in truth, he's a lecherous womanizer hiding behind a good-guy facade. The new guardian constantly bullies the older sister, while favoring the younger sister, Yui, who has a naturally naughty disposition. Seeing the unfair treatment, Yui decides to become a maid to protect her sister. But the man takes advantage of her devotion, using her feelings to manipulate her. With his massive body, he repeatedly violates the delicate girl, breaking her fragile frame. As the assaults continue, Yui gradually loses her sanity, until she forgets even herself.