After losing her husband, Rieko raised her son Kousuke all by herself. As he grew older, Kousuke began awakening to his sexuality and developed impure feelings toward his mother. Rieko noticed this but chose to ignore it and carry on. Then, on the night before Kousuke's wedding—their final night together as mother and son—Rieko tells him, "Since this is our last night together as parent and child..." and decides to give him a final, intimate sex education. But their uncontrollable desires soon drive both mother and son into deeper, forbidden acts.