Satsuki is happy that her daughter has a boyfriend. One day, when she comes home after forgetting something, she finds her daughter bringing her boyfriend, Okamoto. When she peeks into the room to see what's going on, she finds the two of them in an awkward mood after their first sexual encounter didn't go well. Wanting to support her daughter's love life, Satsuki decides to be Okamoto's practice partner so he can gain confidence. However, Satsuki's voluptuous body excites Okamoto more than she could have imagined. They were only supposed to do a quick sex session, but they crossed the forbidden line, and his rock-hard cock lost control like a runaway locomotive.