Tatsuya, who lost his mother, has not been able to get along with Saeko, who became his father's second wife a year ago. With his father, who he relied on, now overseas, Tatsuya has been acting unfriendly towards Saeko. Saeko acts strong without worrying about such things, but... One day, Tatsuya accidentally peeks at Saeko masturbating. Tatsuya cannot hide his surprise. That is because Saeko's finger is stuck in her anus. Tatsuya cannot get the image of his usually chaste mother's wide open and vulgar anus out of his head...