Your sister has caught on that you've been stealing her panties to jerk off with. She confronts you to call you out. Do you think you're going to get away with being such a pervert? No, she has plans for you. She gives you the pair she's wearing to watch as you use them, then she humiliates you while you stroke, telling you how she's going to use this information against you for the rest of your life. You don't want everyone to know about this, do you? Well, then you're going to have to do everything she tells you to from now on.