Flip her and fuck her till she begs you to stop

She's had her orgasm, so now it's your turn. While she's still gasping from her surge, you roll and twist on the couch, still firmly embedded inside her pussy. Heather ends up laying on the couch with you on top of her. You begin plundering her cunt with strong, solid thrusts. Your girlfriend's younger sister whimpers as she heads toward another orgasm.

She pulls your head to her mouth and kisses you deeply, then screams into your mouth. You can feel her pussy muscles pulsing around your driving shaft. Her body shakes on every impact of your groin to hers, your large cock drilling completely through her. Heather's very tight, but so wet that you have no trouble pounding her hard. Her legs are pulled around your body, and her fingernails are scratching the hell out of your back, but you are in nirvana, your cock sending intense pleasure throughout your nervous system. It sometimes takes you awhile to cum, so you just keep going, knowing she'll probably just keep having orgasms until you're ready.

"Omigod! Omigod! Oh! My! God!" she screams, after breaking the kiss. "I'm still cumming! Don't stop! I never want to stop cumming! Fuckfuckfuckfuckfuck!" Then she screams again. You keep thrusting into her nubile body, but you think of baseball and mowing the lawn, because you decide you want Heather to beg you to cum inside her. Maybe if she has another five minutes of orgasming, she'll cave.

In another minute of hard writhing and groaning, Heather is gibbering unintelligibly. You maintain your relentless, steady fucking, enjoying every second. Then your girlfriend's sister begins to whimper. You know she's close to pleading with you.

After another minute, she speaks up, her voice weak and breathy, "You have to cum. I can't take it any more. I can't stop cumming."

"What? I can't hear you?"

"Please! Please cum! Unh!" Her whole body convulses in an even harder orgasm.

"Where?"

"Please cum inside me! You have to cum in my pussy!" She shouts again.

Now you're ready. You speed up, causing Heather to shriek as her climax redoubles. Your cum quickly rises in your cock, and you wait until just as it shoots out, then bury your cock as far inside Heather as you can. Your cum boils out of your shaft, shooting far into her womb. You've been saving this up, and it takes you a long time to stop spurting. Your body rocks, and your eyes roll back in your head as the biggest orgasm of your life wracks your body and mind. The two of you groan out your mutual release.

Finally, you collapse on top of her, sweating profusely. The couch is uneven, and the two of you accidentally roll off of it. Heather lands on top of you, her lungs working overtime to replace oxygen in her body. She appears to have passed out.