Masako, the mother, was caught by her son Tatsuya in the act of cheating with her husband's younger brother. Witnessing that shocking scene, Tatsuya begins to see Masako not just as a family member, but as a woman. That night, Tatsuya makes Masako wear revealing lingerie and enjoys humiliating games that stir her shame. The mischief grows bolder each time, and today brings yet another new development.