Takashi and his wife Kanon have been married for two years. They wanted to have a child, so Takashi abstained for a month so that he could make healthy sperm according to the time just before the ovulation day when it was easy to get pregnant. On the other hand, Kanon's older sister Megumi usually travels around the country as a cabin attendant, and she has been having trouble making children with her husband. Megumi, who wants a child before her sister, comes to seduce Takashi when her sister's couple's planned child-making date approaches, and she takes away the sperm that she has collected.
