Why leave home? (Gwen’s ass)

John made his way downstairs to the living room, Swapinator in hand and his mind racing with possibilities. As he entered, his gaze was immediately drawn to the couch where his bodacious twin sister Gwen was splayed out. The blonde bombshell was clad in a tight white crop top that struggled to contain her massive 34D breasts, with her plump tits threatening to spill out at any moment. But it was her lower half that really made John's jaw drop.

Gwen's long, shapely legs were on full display a she laid on her stomach, those thick toned thighs threatening to rip her skimpy shorts that clung obscenely to her wide fertile hips. The tight fabric was pulled taut across her plump rear end, the outline of her juicy ass cheeks visible for all to see. John felt his face flush red hot as he shamelessly drank in the sight of his sister's tantalizingly curvy figure, unable to peel his eyes away from those delicious childbearing hips.

"See something you like, dweeb?" Gwen sneered without looking up from her phone, clearly aware of her brother's lustful staring.

John swallowed hard, his scrawny hand gripping the Swapinator tightly as he aimed it squarely at Gwen's lower half. "You know what...I think I do," he muttered under his breath. Picturing his sister's thick thighs, wide hips and that fat ass in his mind, John zapped Gwen and then himself.

***ZAP***

There was a bright flash as the Swapinator hummed to life. When the light faded, reality had been retroactively rewritten. John looked down in a mixture of shock and arousal to find his lower body had been completely transformed! His scrawny legs were gone, replaced by a pair of thick, shapely thighs and wide, fertile childbearing hips that were unmistakably feminine. He ran his hands down the soft, toned curves of his new lower half in disbelief, giving his plump rear end an experimental squeeze. It was real - he had Gwen's body from the bellybutton down!

But the biggest surprise was how his clothes had adapted to his new figure, with his baggy sweatpants and boxers stretching obscenely across his thick thighs and clinging to his fat ass like a second skin. John couldn't believe his luck - he could experience the feeling of his sister's insane curves without anyone being the wiser!

Gwen, meanwhile, remained oblivious to the swap as she continued scrolling on her phone, those long feminine legs of hers were now scrawny pale and masculine. "You're fucking disgusting, perving on your sister.” she said dismissively, not even looking up.

A wicked grin spread across John's face as he shamelessly drank in the sight of his new hips and ass, giving his plump cheeks a firm squeeze. This was going to be fun.