Hiroko arrives at a beautiful mansion as a private tutor for a young girl named Yuki. After drinking some tea offered by Shizuka, Yuki's sister, Hiroko falls unconscious. Hiroko finds herself tied to a bed, naked. She finds herself being sexually molested by Yuki and Shizuka - they use sex toys and perform various sex acts. Soon, the shocking family secret is revealed. Will Hiroko be able to defend herself? What will happen to Hiroko? Experience the sexual debauchery of the two sisters as they use Hiroko as their living sex toy.