Chapter 18: Temptation Behind the Curtain
Saturday morning’s workout had been heavy, but the real endurance test began the moment we stepped out of the gym. Instead of heading straight to the car, Sophia dragged me into a fitness apparel store on the very same block. The store was considerably busy for a Saturday. My sister exuded that chaotic energy of hers; the tight black lycra shorts perfectly accentuated her curves, and her gym top left her sweaty skin glistening. The scent of sweat mixed with her perfume was a dangerous trigger, and the way she paraded down the aisles, drawing stares, was already pushing me to the limit.
Sophia selected a set of athletic lingerie and two pairs of tiny workout shorts. She looked at me with those eyes gleaming with pure, voyeuristic malice.
"Lucas, come with me? I want you to see if the fit is right," she asked, her voice dangerously soft, pointing toward the back of the store.
I didn’t answer; I simply followed her to the changing room area. The space was divided into small stalls, whose entrances were protected only by thick fabric curtains that hung just down to ankle height, leaving feet completely visible to anyone passing through the corridor. We stepped into the last stall. The space was tiny: just a large vertical mirror, a wooden bench, and the two of us, squeezed together and radiating post-workout heat.
The moment the curtain closed, Sophia didn't waste any time. She threw herself against my chest, pulling me by the collar of my hoodie, and crashed her lips into mine in an absurdly wet, hungry, and violently needy kiss.
"Lucas..." she whispered between our lips, her breath hitching. "I can hear the sales assistants talking right there by the clothing rack. If we make any noise, everyone will find out."
The idea of the danger and the sheer exhibitionism of being inches away from strangers made my cock snap completely rigid inside my shorts. Sophia noticed the bulge against her thigh and smiled audaciously. Without taking her eyes off me, she turned her back, bracing both hands firmly on the wooden bench, arching her round ass directly toward the mirror.
With a swift, shameless movement, she pulled her lycra shorts and panties down to the middle of her thighs all at once.
"Fuck me while looking in the mirror, little brother... but it has to be in silence," she challenged in a husky whisper, staring at the reflection of my eyes.
My hands slid straight to her waist, gripping the firm flesh. I untied the drawstring of my fleece shorts, letting them drop along with my boxers. My member surged, pulsing with arousal. I stepped forward, pressing my sweaty chest against her back, and positioned the head of my cock right at the entrance of her intimacy, which was already completely soaked and warm.
Without warning, I thrust my cock inside all at once, burying it to the hilt in my sister's eager tightness.
"Mmhff...!" Sophia let out a sharp gasp but instantly covered her mouth with both hands, her eyes widening in the mirror. Her entire body trembled at the sudden fullness and the fear of getting caught.
I began to pump into her right there. The pace had to be controlled, which made everything even more torturous and pleasurable. With every deep thrust, her inner walls squeezed me with absurd force, stimulated by the adrenaline of the situation. The only sound in the cubicle was the soft friction of our sweaty bodies and our muffled breathing.
Suddenly, firm footsteps echoed down the changing room corridor. A sales assistant stopped right in front of our stall, just inches from the curtain.
"Hello? Do you need any help with the sizes in there?" the employee's voice rang out clear and loud.
I froze with my cock buried deep inside Sophia. My sister dug her nails into the wooden bench, holding her breath, her hips locked against mine. I could feel her pussy pulsing and contracting violently around my member from the shock and panic. The pleasure of that tightness almost made me cum right then and there.
Sophia cleared her throat, trying to keep her voice as normal as possible, even though her eyes were rolling with sheer ecstasy.
"N-no... thank you! I'm just trying on the shorts... they fit great," Sophia replied, her voice coming out a bit shaky at the end.
"Oh, wonderful! Just call if you need anything," the sales assistant said, and the footsteps faded down the corridor.
As soon as the sound of the footsteps vanished, Sophia let out her held breath in a heavy, whimpering sigh. She looked back over her shoulder, her pupils completely dilated.
"My God, Lucas... my body almost exploded just now. Come on... fuck your sister fast, I can't take it anymore!"
That near-catch was the final fuel. I gripped her hips tightly and shifted into long, fast, relentless thrusts, ignoring the risk entirely. Sophia whined quietly against her own arm, biting her skin to keep from screaming as I pounded her from behind. I watched in the mirror the obscene image of my cock entering and exiting her right in the middle of a public changing room.
Within a few seconds, her inner muscles began to spasm violently. Sophia arched her back, her eyes rolling back as she fell into a shattering, silent orgasm, melting against the bench.
The tight grip of her climax pushed me over my own edge. I held her even tighter, driving my cock as deep as I possibly could into my sister's womb, and let everything go. I came abundantly, spilling hot, deep spurts inside her, filling her completely while she shook.
Our bodies were still connected, my member slowly softening inside her as we caught our breath in absolute silence. I could still feel the sweat dripping down my chest and the warm semen overflowing down Sophia's bare thighs, when the harsh clatter of metal rings sliding across the curtain rod shattered the quiet of the cubicle.
The curtain was ripped open all at once, exposing us completely to the store corridor.