She's now free for your use, always.

"So from now on," you begin, and she looks at you with tears flowing down her face, "you're always gonna be free for me to use, however I want. You have to do whatever I want you to do, whenever I want you to do it. You can't tell anyone about it, either." Her face screws up in anger, and she spits at you. "Fuck you, James, fuck you! I'm gonna tell-" You've had enough of that. Time to test it out.

"Come here and suck my cock, you got it dirty." She stands up and her face is stricken with fear- "What? Why am I moving, I don't want this!" With more protests, she turns and positions herself to suck your cock, weeping as she begins to slobber all over you. You can tell she hates the taste of herself mixed with your come, and you moan appreciatively. "You're lubed up and ready for me to fuck your ass," you murmur, and she lets out a little surprised squeak as she feels the change in her asshole. "Stop sucking and get on your hands and knees," you say. She stops sucking, and starts pleading with you again. "Please, please, James, please, I'm sorry, I'm sorry, please don't, there's no way it's gonna fit, please don't-" You ignore her, moving behind her and pulling apart her cheeks. Her pink asshole is shining with wetness, and you test the tightness by sliding a finger in. It goes in easily, and your sister yelps at the intrusion. "P-pleeease-" You grin, slapping her ass. "You don't have to beg, I'm gonna fuck you, you greedy slut." She cries loudly as you postition your cockhead at her entrance before pushing in, groaning and seeing stars as the silken tightness surrounds you. Even with your command, it's a tight fit, and you moan loudly. "Ohhhh, fuck, your ass feels so good... maybe it's because we're twins, but it's like your ass was made for my cock..." You don't waste any time, immediately fucking her fast and hard, giving her no time to get used to the massive length inside her. She's making little yelps and moans and you're surprised when her ass tightens around you and you feel her pussy spasm against your balls as they slap against her. Melissa just came from your brutal ass ****. The thought of this is too much and you spill another load inside of your little sister. You pull her hair and grind against her ass, intending to shove your thick cum deep in her guts.

You pull out with a sigh as you finally come down from your orgasm. A little bit of your load dribbles out of her ass and pussy, and you give her ass an affectionate pat.

"You can go back to sleep now. In the morning, though, you're going to wake me up with a blowjob."

With that, you leave your thoroughly **** sister, heading back to your room. Your house is quiet- obviously your parents didn't hear their children fucking loudly. You grin and head to bed. Life is much better now.