Koji, who was left alone by his wife's homecoming birth, offered to take care of her sister-in-law, Mizuki. Koji, who is struggling to balance work and housework, happily accepts, but ends up taking a bath with Mizuki, who even tries to take care of her bathing. A meat stick that reacts to Mizuki's beautiful nude body. Mizuki noticed it and forcibly said, "Did you get an erection with me? I'm happy...".