Seeing his younger sister seducing and having sex with her stepfather, whom she secretly adores... HUNTB-520

My sister fell in love at first sight with the man who recently became my stepfather, frequently seducing and having sex with him. I accidentally witnessed this, but couldn't remain silent because I was worried about my mother. My sister came to my room, wanting me to keep it a secret, but suddenly started forcing oral sex and seducing me, which aroused me uncontrollably... I was forced to make a devilish deal. Even if she were my own family, I couldn't resist sleeping with her for free! I never imagined my sister was such a lewd woman... My stepfather and I were both controlled by her.