After her divorce, Mirei devotes herself to her work as a sales lady to support her son. One day, she sees her son walking with his girlfriend. At breakfast, she brings up the topic, but her son seems depressed. When she questions him, he says, "I tried to have sex, but I couldn't get my penis in properly." Mirei gives her son a sex education, saying, "Mommy will teach you how to have sex properly," but before she knows it, she is excited by her son's dick and feels it...