When I went back to my wife's parents' house, my sister-in-law and her husband were also there. I was attracted to my sister-in-law's bust, which was bigger than my wife's, and I couldn't help but stare at her. I fantasized about doing all sorts of things with my sister-in-law. Then, my sister-in-law Kokoro seduced me! Even though we're step-brothers, this is incestuous... My sister-in-law was excited to steal me from her sister, so I got excited and stole my brother-in-law's.