Seigo and Miki, who are in their second year of marriage, were trying to conceive by abstaining for one month and releasing the accumulated sperm to coincide with the fertile period just before the ovulation date. Miki's older sister Mina, who lives in the neighborhood, also wanted a child, but she was in a sexless state due to her husband's ED and busy work. Mina, who wants to get pregnant before her sister, came to seduce Seigo in a braless appearance with her nipples sticking out on the scheduled day of her sister's couple's child-making, and she endured it and finally uprooted the sperm that had accumulated.