Satsuki is happy that her daughter has a boyfriend. One day, when she returns home after forgetting something, she finds her daughter has brought her boyfriend, Okamoto, along. Peeking into the room to see how they are doing, she finds the two of them in an awkward state because their first attempt at sex didn't go well. Wanting to support her daughter's romance, Satsuki decides to become a practice partner so that Okamoto can gain confidence. However, Satsuki's voluptuous body excites Okamoto more than imagined. What was supposed to be just dry humping crosses the forbidden line, and his rock-hard erect cock loses control like a runaway train.
