Three months have passed since the sister and her brother-in-law, who lost his job, started living together with their husband. The brother pays his sister a little money as a housekeeper. One night, the brother feels something strange in his crotch as he watches his sister comforting her depressed brother-in-law. One morning, the sister removes the blanket to clean the room and feels something strange when she sees her brother's erect penis. One day, while drinking together, the brother discovers that the brother is paying a fair amount to prostitutes. "What? You're paying that much? What a waste! Give me that amount lol ahahaha lol" the sister says, which puzzles the brother, but when he tries to negotiate with her, she says, "Huh? If you're paying me, that's fine lol?" As they check their compatibility in a strange manner, fuelled by the alcohol, they start to get excited and can't stop... Although they are both open to it, the sister and brother cross the line and things escalate...