Shoko has always forced herself to act satisfied with her husband's tiny, half-hard cock and premature ejaculation, even masturbating afterward to make up for it. When he meets a hung, insatiable adult student boasting about his stamina, he devises a substitute-cock plan: the stranger will replace only his penis while the room is dark and Shoko is bent over. The instant they switch, she screams and climaxes again and again in ways her husband has never seen.