You left your door open while you were jerking off, what a stupid idea. Your step-sister comes in and catches you, oh you're in big trouble, she's ecstatic at the thought of telling on you. You say you'd do anything to avoid another grounding, and she smirks as she thinks of something that may persuade her otherwise. She wants you to eat your whole load, not just a little bit, every single drop, she won't be happy until you fulfil the task at hand, whether you like it or not.