Shinichi, who has a wife and child, lives every day thinking of his mother, Eri, as a woman. One day, unable to suppress his overflowing sexual desire, he decides to go on a trip to a hot spring with his mother, thinking that it would be just once. Eri thought her son's story of mother and son making love was a joke, but when she saw a penis for the first time in a long time, she gave herself over to the waves of pleasure. Receiving her son's hot milky liquid deep inside her body, she was unable to resist the overwhelming pleasure. A mother-son incest story where forbidden moans echo in a hot spring deep in the mountains.