Junichi and his wife Miki, who have been married for three years, are actively trying to get pregnant together, with the husband abstaining from sex for a month to coincide with the period just before the wife's ovulation when she is most likely to become pregnant. Meanwhile, Miki's older sister Maria, who lives in the same apartment building, is also unable to have children due to her husband's erectile dysfunction, but she wants to have children before her sister does, so when the due date for her sister and her husband to have a baby approaches, she comes over in revealing clothes to seduce Junichi and steal all of his sperm.