Cumming Deal With Sister

You caught your sister masturbating with a vibrator. You are going to tell mom unless she lets you watch her cum. She is so grossed but but she loves the vibrator too much and lets you see. Then you are jerking off and cum to her while she cums with a vibrator. You are still hard and wanting more. She has to go along with this in order to keep her vibrator. She has sex with you and then you tell her about a cumming deal. She has to cum for you anything you want her to in order to keep her vibrator a secret from mom. You order her to cum again with her vibrator.