Two orphaned adult sisters are adopted by a wealthy man who hides his insatiable lust behind the mask of a kindhearted guardian. He torments the sickly older sister at every opportunity while lavishing his lustful attention on the younger one. To protect her sister, Yui becomes his maid and agrees to serve him. Exploiting her devotion, the hulking adoptive father pins Yui beneath him and rapes her over and over. Violated so brutally that her slender body seems ready to break, Yui gradually loses her grip on reason.