She can't resist

Keira slowly opens the door and near stumbles inside, and what a sight she is.

Her legs are unsteady with need, her grey sweatpants soaked so thoroughly it looks like she pissed herself, her face is blushing bright red and she's panting like she's just run a marathon.

"h- how long have you had err, a penis?" She says, unable to keep her eyes off it as she asks.

"I’ve had it ever since I was born" you say grabbing your massive cock at the base and pointing it towards her.
"You wanna come feel it?" you finish, playing shy.

She takes the bait and starts waddling over. Her gait made awkward as she clumsily attempts to make her sodden pants and obvious need anything other than clear as day. Her efforts are, for lack of a better word, adorable.

Her nervous hand finally makes contact with your perfect weapon. Despite her having tended to herself earlier, her grip is ever so slightly colder than your cock. A fact that changes quickly as your massive member radiates heat into her gentle embrace.

Your sister stares transfixed at your cock, her eyes glued to the ludicrous comparison between her dainty digits and your ridiculous rod.

You can almost hear a gush as your sister's pants get somehow wetter, and you are now more certain than ever that she's yours.

Grabbing the back of her head you pull Keira into a deep kiss, your fearsome endowment staining her shirt with its drooling lust all the while.

You can't wait any longer.