After her husband's death, Rieko raised her son Ko-suke single-handedly. As Ko-suke grew up, he began to harbor perverse feelings towards his mother as he awakened sexually. However, she pretended not to notice and continued living her life. On the eve of his marriage, unable to release his desires through masturbation alone, Rieko told him, 'Tonight is our last night together as mother and son...' She gave him a final lesson in sex education. But their uncontrollable desires drove them towards even more forbidden acts...
