The house was empty except for us. Mom and Dad had left for the weekend, and my little sister, now twenty-one and home from college, was already walking around in nothing but a thin tank top and panties like she owned the place. I watched her ass move as she bent over the fridge, those cheeks barely covered, the fabric riding up. My cock twitched right away. We'd never crossed the line before, but the way she looked at me lately said she wanted it.
"Stop staring, perv," she said, but her voice had that teasing edge. She straightened up with a soda and turned to face me, nipples hard against the cotton. "Or do you want to do something about it?"
I didn't answer with words. I grabbed her wrist and pulled her close, my free hand sliding down to squeeze that firm ass. "You know exactly what I want, sis. That tight little hole you've been teasing me with."
She gasped but didn't pull away. Instead she pressed against me, feeling my hard cock through my jeans. "Fuck, you're serious. You really want to fuck your own sister in the ass?"
"Damn right I do." I spun her around and bent her over the kitchen counter. Her panties came down fast. Her pussy was already wet, but I wasn't going there first. I spread her cheeks and spat on her asshole, rubbing the slickness in with my thumb. She moaned and pushed back.
"God, that's dirty," she breathed. "Do it. Stick your cock in my ass."
I freed my dick, thick and throbbing, and pressed the head against her tight ring. No lube beyond spit and her own juices, just raw and direct. I pushed. She was tight as hell, gripping me, but she took it. Inch by inch my cock sank into my sister's ass while she clawed at the counter and cursed.
"Fuck, it's big," she whined. "Don't stop. Fill my ass."
Once I was buried balls-deep, I started thrusting.
Hard, steady strokes that made her cheeks slap against me. The sound was filthy—skin on skin, her moans, my grunts. I reached around and rubbed her clit while I pounded her ass, feeling her hole clench around my shaft.
"You're such a slut for your brother's cock," I growled. "Taking it in the ass like you were made for it."
"Yes," she panted. "Harder. Fuck my ass harder."
I gave her what she asked for. Long, deep strokes that stretched her open. Her asshole gripped me like a fist every time I pulled back. Sweat ran down my chest. I slapped her ass cheek and watched it redden, then did it again. She pushed back to meet every thrust, begging for more.
We didn't last long like that. Her fingers worked her clit faster and she came first, ass spasming around my cock, juices dripping down her thighs. The squeeze pushed me over. I buried myself to the hilt and unloaded, pumping thick ropes of cum deep into her ass. She stayed bent over, breathing hard, while I slowly pulled out and watched my load leak from her stretched hole.
We didn't talk much after. She just turned around, kissed me rough, and whispered, "Bedroom. Round two. I want you to fuck my ass again until I can't walk straight."
That weekend we barely left the house. Every chance we got, I had my cock in her ass—on the couch, in the shower, on her bed with her face in the pillow and her cheeks spread wide. She learned to take it deep and fast, learned to beg for my cum inside her. By Sunday night her ass was sore and used, but she still climbed on top and sank down on me one last time, riding my cock with her back door until I filled her again.
We both knew it was wrong. We both knew we'd do it again the next chance we got.
