I caught my sister jerking her cock in the bathroom again last night. She was standing there naked, legs spread, that thick piece of meat in her fist, pumping it slow and hard while she stared at herself in the mirror. I didn't knock. I just walked in, shut the door, and locked it behind me.
"What the fuck, Mark?" she hissed, but she didn't let go. Her cock was already leaking, shiny at the tip, and her hand kept moving even as she glared at me.
"Shut up, Lisa," I said, stepping closer. "You've been teasing me with that thing for months. Hiding it under skirts and then bending over so I can see the bulge. I'm done pretending."
She bit her lip but didn't stop stroking. Her tits bounced with each tug, nipples hard. "You want it? You want your sister's cock?"
I dropped my pants right there. My own dick was rock hard and pointing at her. "Yeah. I want to fuck you with it. And I want you to fuck me back."
Lisa moaned low and dirty. She turned around, bent over the sink, and spread her ass cheeks. Her cock hung heavy between her legs, balls tight. "Then get in here and eat my ass first. Get it wet so you can slide that dick in me while I stroke this cock."
I dropped to my knees and buried my face between her cheeks. Tongue straight to her hole, licking and spitting, getting it sloppy. She reached back and grabbed my hair, grinding back on my mouth while her other hand kept working that fat cock. "Fuck yes, little brother. Tongue fuck your sister's asshole."
When she was dripping, I stood up, lined my cock up, and shoved in. She was tight and hot, gripping me as I started pounding. Every thrust made her cock swing and slap against the cabinet. She moaned louder, jerking herself faster.
"Harder," she demanded. "Fuck me like you mean it. Fill your sister's ass."
I grabbed her hips and slammed into her, balls slapping. She came first, shooting thick ropes of cum across the sink and mirror, her asshole clenching around my dick. That pushed me over. I buried myself deep and unloaded, pumping my load into her.
We didn't stop there. She spun around, still hard, and pushed me against the wall. "My turn." She spit on her cock, lifted one of my legs, and pressed the head against my hole. "You wanted it.
Take your sister's cock."
She pushed in slow at first, then buried it. The stretch burned but felt so fucking good. She fucked me raw and deep, one hand on my throat, the other stroking my cock in time with her thrusts. "You love it. You love getting fucked by your sister's big dick."
We came again like that, her flooding my ass while I shot across her stomach. After, we didn't talk about stopping. We just moved to the bedroom, locked the door, and kept going all night. Her on top, me on top, her cock in my mouth, mine in hers, swapping loads until we were both sore and sticky.
By morning we knew this wasn't ending. It was just the start of us using each other every chance we got.
