A mother and son go on a trip to a hot spring. While they are in the mixed bath together, the son feels a sense of femininity in his mother's body, which he hasn't seen in a long time, and gets an erection. Seeing her son's embarrassed appearance, the mother feels an irresistible love for her son and accepts his body. The mother is pounded hard by his young, rock hard cock, and is drowned in the pleasure she hasn't felt in a long time.