Go get what you want

Upon entering her room, you found her lying face-down, looking around the internet on her laptop and cut off from the rest of the world by the music blasting through her earphones. Looking at her lying there, you hesitated for a minute. You had made your sister to be the sweetest person in the world, and now that your memories had changed to include her, you were suddenly struck with brotherly protectiveness, despite the fact that you know you made her just a few minutes ago. Her position on the bed, though, combined with her outfit, gave her a major case of camel toe, and as your dick hardened, your original intent reasserted itself.

Grinning mischievously, you gave a loud shout and dove onto the bed, straddling her legs and wrapping your hands around her sides, quite effectively scaring the shit out of her. Shrieking, she tuned over underneath you, and upon realizing who it was, her expression changed to pissed off, though a little relieved that it is only you and not some sex-crazed criminal.

"You asshole!" She exclaims, "You almost gave me a heart attack!"

"Sorry sis," you reply. "But you had it coming. Vengeance!!" you cried, sitting up slightly. "I've thought of something for us to do, if you're interested." you add, moving your hands up to rest on her shoulders, your body still over her's.

"Well? What do you want to do?" she asked.

"You," you state matter-of-factly. "I want to spend the day doing whatever I want to you." You stomach tightens into a knot as you see your sister's face change from a picture of innocence to slightly quizzical, slightly sultry look, but you've already crossed the line. Pinning her arms to the bed, you lean in and give her a passionate kiss, directly on the lips. She moans into your mouth, kissing you back. You're afraid of what she might say so you don't take your lips off of hers for a bit, until she reaches up and pulls one of your hands down to her clothed breast. You can feel her warm, young body writhe beneath you and as a result, you can feel yourself getting harder. You wonder briefly if she can feel it to, and press you member against her in order to find out.

Finally needing to breath, you both pull back.

"Why didn't you just say you wanted to fuck?" She asks, disbelief clearly in her voice. "You didn't have to sneak up on me like that. Next time just ask," she added, reaching down and encouraging you to fondle her.

"Well, sis," you begin in a soothing voice, "For a very long time I've imagined what it would be like to have you. I've wanted to kiss you, hold you, and fuck you for so long that I can't hold it in any longer."

"Let me guess: 'but you're my sister' is what you're gonna say, right?" she put in. "I'm still a woman, you know, and mom didn't raise me to be some impolite frigid bit..."

You cut her off before she could say another word, planting yourself back on her lips and humping her a bit through your respective clothes, while you continued to fondle her. With your new power you can play out your fantasy without any care at all, and no consequences; she's your perfect sister, just how you made her.