His mother, Kayo, has been concerned about his son Masateru's behavior since he went to a club training camp.According to her husband, it seems that it was because she had a wet dream during the training camp and was ridiculed by her teammates.Considering her son who has little knowledge of sexuality even though she is around her age, Kayo secretly thinks "At least just the method of ejaculation ..." and gives Masaki a sexual treatment with a fellatio.However, her half-hearted help turned her back on her, and Masateru begged for further sex education.Finally, it was decided to perform "sex practice" by mother and child.