The trip to the hot springs was canceled by her boyfriend, so the sister brought her younger brother along because it would be a waste. Since she was supposed to go with her boyfriend, of course they were sharing a room and bathing together. She had never noticed her sister's huge breasts before, but now he was getting an erection! He tried to hide it, but his sister swayed her breasts as she approached him. He thought he would get in trouble if she found out… but his sister couldn't help but stare at his erect penis.
