Satsuki is happy that her daughter has a boyfriend. One day, when she returns home to get something she forgot, she finds her daughter with her boyfriend Okamoto. Satsuki peeks into the room and sees the two awkwardly struggling with their first time having sex. Wanting to support her daughter's love life, Satsuki decides to become Okamoto's practice partner to boost his confidence. However, Satsuki's voluptuous body excites Okamoto more than expected. What was supposed to be just frottage crosses the forbidden line, and his rock-hard cock thrashes about like a runaway locomotive.
