One day, while Maki was doing the washing up, the woman next door came to visit. For some reason, her son Shingo was standing behind her... When she asked her about it, she learned that Shingo had been warned by the woman when he was trying to take off his underwear. Since they were close, nothing bad happened at the time, but Maki was very confused by her son's actions. Without Maki's knowledge, her son Shingo had reached the age where he was interested in women. Since his father was away on an overseas assignment, Maki decided to use her body to start teaching him sex education.