In their second year of marriage, Seigo and Miki are trying to conceive by abstaining from sex for a month and releasing the sperm they've saved up during the fertile period just before ovulation. Miki's older sister Mina, who lives nearby, also wants a child, but her husband has erectile dysfunction and she's busy with work, so they're not having sex... Wanting to get pregnant before her sister, Mina comes to seduce Seigo on the day her sister and her husband are due to have a baby, wearing no bra and revealing her nipples, and takes all of the sperm he's saved up after enduring it all...