"I don't know, babe... Maybe this is wrong...", you retract backwards, away from your sister.
"I think.. that you should totes just fuck me already", your GF/Sister counters with her bitchy voice as she starts to unbuckle your belt and open your jeans with a dainty hand, her long fingernails now tipped with black nail polish, your sister's favorite.
You stopped fighting, the part of you that has always desired your beautiful, if shallow and bratty, sister, getting extremely turned on by the sight of her pulling out your dick from your pants with her small, manicured hand.
You stare into her eyes, now ocean blue, completely different from your girlfriend's original eyes, yet still so similar, as she clambers on top of your dick and starts riding you.
She starts moaning in her high pitched voice, and her wide hips press her now beautiful, heart shaped rear into your groin. You glide your hand across her fit stomach and her hefty D-cup breasts, making her shiver with lust.
"Yes, big bro. Fuck me like the fucking whore I am!" your GF/Sister screams in pleasure as she plays with her now wavy, dirty blonde hair, upon which you release your semen.
“OMG, that was, like, super hot. Thanks again for helping me get off before practice, big bro.” Your girlfriend/sister says as she cuddles up next to you.
Picking up her role playing queue, “Anytime, sis.” Grabbing her by the ass and pulling her in for a kiss.
“So, like, what now?” She says, placing her manicured hand on your chest and looking into your eyes.