Targeted mother's anus

Tatsuya, who lost his mother a year ago, has been unable to get along with Saeko, who became his father's second wife. Tatsuya's father, who he relies on, has also gone abroad, and Tatsuya ends up being unfriendly towards Saeko. Saeko acts bravely without worrying about such things, but... One day, Tatsuya accidentally watches Saeko masturbate. Tatsuya couldn't hide his surprise. That was because Saeko's finger was stuck in his anus. Tatsuya can't get the image of his usually chaste mother's open, vulgar anus out of his mind...