Mother-in-law's pain

Mika married into the Yamaguchi family as his second wife. Mika and her ronin student son Tetsuya have a rather aloof relationship, perhaps because they have only been living together for less than a month. One day, Tetsuya spies on his father and stepmother having sex. A gentle face during the day and a lecherous face at night. From this day on, Tetsuya's head is filled with thoughts about Mika. Tetsuya's lewd fantasies about his mother-in-law keep coming out one after another, and he finally reaches the limit of his patience...