The world has come to an end... everything is covered in ashes. Fortunately, Taro manages to escape to a shelter where 10 women have already taken refuge, and he is welcomed as the only male survivor. Some of the women then invite Taro, who is the only one with male genitalia, out and ask for sex. Word of Taro's prowess quickly spreads throughout the shelter, and a strong reproductive instinct spreads among the women. In search of sperm, Taro has sex with the women every day. This is the beginning of a chain of sex days leading to a future where sperm will be extracted in a dream communal life...