Thomas was getting close, he could feel the pressure building. He grunted out a warning to Isabelle, and she insisted that he cum inside of her. Obliging, he pulled back before slamming forward to pump it deep inside of her.
He closed his eyes, and suddenly he felt a shift. He felt himself laying on his back, legs up, hands on his shoulders. He felt something inside of him, an intense pleasure and pressure in his loins. And then he felt something warm shooting inside of him. His eyes shot open as he cried out in shock and pleasure, looking at... himself. He was getting fucked by his own body, pumped full of his own cum. Which meant that he...
Panting and horny, he looked and saw that he was covered in yellow fur, that there was a pair of breasts on his chest, that his thick, feminine legs were wrapped around his own back. He was in Isabelle's body, and presumably she was in his, though she seemed to be too shaken by the afterglow to realize what had happened.
A moment passed, his body idly humping him, before it blinked and registered what was happening.
"Wh-what?!" his voice said, though the tone sounded very familiar to Isabelle's speech patterns. "Wh-why am I looking at myself!? Why am I so... big!? And what is... is this..." She paused her questioning to moan, unable to stop thrusting into her own body. She bit her lip, looking over her form, and Thomas could only imagine what was going through her head.
Thomas was concerned about this turn of events... but also couldn't think clearly. This body hadn't orgasmed yet, and it was craving it so badly. He needed release to think clearly. So, he squeezed those thick legs around the back of his body tighter, locked eyes with Isabelle, and said "Don't hold back. Just do what your body tells you to. Fuck me."
With the permission granted, Isabelle seemed all too willing to give into her new male urges, gripping your shoulders and resuming the pounding. It felt... incredible. Thomas submitted himself to taking his own cock as it plunged into his new pussy again and again. Pressure began to build. Neither of them were used to their new bodies and hormones, and soon enough...
The two cried out in unison as both came, Isabelle pulling out at the last second and shooting cum all over her own body. Thomas felt it splattering him, even tasted some that managed to get into his moaning mouth, loving the sweetness. Some part of him wanted more, wanted to suck off his own cock, fueled by his lust addled mind.
Isabelle slumped on top of Thomas, and the two cuddled in each other's bodies, basking in the afterglow, unable to fully think about what had just happened. When their lust faded and the post sex clarity hit, they would deal with whatever this was...