Rikka, the prickly adult younger sister of his girlfriend, summons him to a love hotel and takes control in an intimate seduction. Claiming it is a safe day, she tells him to keep the secret and creampie her again. They spend the afternoon, evening, night, and following morning tongue kissing and having intense sex, even losing track of time while his girlfriend works from home. Though he knows it is wrong, he gives in to the forbidden pleasure and fills her repeatedly.