The young couple Takashi and Kannon have been married for half a year, they have always wanted to have a child, but Kannon can't because she has infertility. Coincidentally, Megumi, a flight attendant and Kannon's older sister, is also looking for a baby while the two of them can't do it together often due to work circumstances. The story began when Megumi visited her sister's house, after learning that Takashi was saving a large amount of sperm for his wife, she asked her brother-in-law to help her because it was the day she ovulated. Although she constantly refused and advised her that it was completely wrong, she didn't care, on the contrary, she violently caressed the boy and even raped him when her sister didn't notice. This will continue to happen in the ovulation days of next month if this lewd sister is not pregnant.