The change hit us both on the same night, right after Mom and Dad left for their anniversary trip. I was twenty-three, Jake was twenty-five, and the old house felt too quiet until the heat started crawling under our skin. It began in the living room while we were watching some dumb movie, beers in hand. First came the itch along my spine, then the ache in my bones like they wanted to stretch and crack open. Jake groaned beside me on the couch, his shirt already soaked through. "Fuck, what the hell is this?" he muttered, voice dropping lower, rougher.
We stripped without thinking, clothes hitting the floor in a pile. Fur sprouted in patches—thick, dark gray for him, tawny and sleek for me—pushing out from our pores while our faces pushed forward into muzzles. Claws replaced nails, tails burst from the base of our spines, and our bodies thickened with muscle and feral power. The transformation burned, but it also made everything between my legs throb and drip. Jake's cock swelled huge and red, knot already forming at the base as it jutted from its sheath. My own cunt clenched and leaked, the scent of our arousal thick and musky in the air.
"Look at you, sis," Jake growled, his new wolfish features twisted in lust as he grabbed me. His paws were rough, claws careful but insistent as he spun me around and bent me over the couch arm. "You're dripping for your brother's knot already." He didn't wait. The head of that thick anthro cock shoved into my slick folds, stretching me wide in one hard thrust. I yowled, half human, half new wolf, pushing back to take every inch. The knot popped in with a wet sound, locking us together as he started pounding.
Each slam sent sparks through my transforming body. My tits hung heavy, nipples brushing the fabric while Jake's furry chest pressed against my back. His knot swelled bigger inside me, grinding against my walls, and I came hard, juices squirting around his shaft. But he wasn't done. He flipped me onto my back on the floor, my new tail thrashing, and mounted me properly—missionary but feral, his muzzle on my neck as he rutted. "Take it, little sister," he snarled, hips snapping. "This pussy's mine now."
His cum flooded me in hot pulses, knot pulsing as it pumped load after load deep into my womb. The transformation finished while we were tied, our bodies fully anthro—ears twitching, muzzles locked in a messy, tongue-filled kiss.
We stayed knotted for what felt like hours, grinding through aftershocks, the forbidden heat of incest mixing with the raw animal need. When the knot finally deflated, we didn't stop. We fucked again on the rug, then in the shower where water streamed over our fur, Jake taking me from behind while I clawed the tiles.
By morning we were still changed, bodies sleek and powerful, the bond sealed in sweat, cum, and shared feral hunger. We knew we'd never go back, and we didn't want to.
