Your step sister loved to groom herself. Her skin was always velvety and perfect. Her secret was that she used your sperm to take care of her face. When she first asked for it, it was strange and incomprehensible, but after a while, handing your stepsister a jar of semen every 3 days became the norm. One day your sister came to your room again. This time she needed more sperm than usual. But you didn't have that much for her. So she suggested that you have sex and cum on her face as many times as needed. She needed cum from you any way she could get it. That's why she chooses to fuck her step brother to get care for her face.