On his birthday, Takumi discovers that he is one of the few remaining males in a world facing human extinction. To ensure the survival of the species, he is granted a "Compulsory Conception Permit," which gives him absolute authority to impregnate any woman. Tasked with the mission of mass procreation, Takumi begins utilizing the permit on the women in his life, including his sister Ena and childhood friend Rin, as he embraces his role as the world's designated "sex warrior."