Diagnosed with multiple sclerosis, young researcher Reito Mizuhara is to be put into cryosleep until a cure can be found. Short on time, Reito decides to confess his pent-up feelings to his childhood crush Erisa Tachibana and bids farewell to his family and friends. As Reito goes to sleep and his consciousness begins to fade, Erisa barges into the room and declares that she will wait for him.

Five years later, Reito wakes up to a post-apocalyptic world where 99.9% of the world's male population had been eradicated by the "Man-Killer Virus" four years prior. He is one of a handful of men who have become immune to this virus due to sclerosis treatment. Reito and the other four men are now invaluable assets to humankind and are expected to impregnate as many women as possible. Reito, however, is determined to find Erisa and refuses to make love with any other women. With temptations lurking around every corner, can he hold on to the woman of his dreams?