Nate whimpered as Dave slowly pushed one of his huge, thick cocks into his ass. Soon, the other followed It was far too large for his diminished body, even with its extra elasticity, and every millimetre burned as it inched its way in. But Dave's huge arms were unrelenting, inescapable, slowly but surely pressing him down onto the shaft until he could take it to the hilt.
Nate felt something slimy crawl slither around his neck. He cried out and turned around only to find that it wasn't just Dave's body that increased in size. A wet, fleshy appendage, as long as Nate was tall, slithered out of Dave's mouth. His tongue. The pink tentacle, which seemed to be entirely under Dave's control, licked up around his neck before slithering down his body and wrapping around his pre-pubescent cock. Seconds later, another tongue wound its way around his balls and fondled his ass, simultaneously blowing, rimming and penetrating the defenceless boy.
Nate was trembling from the assault of pleasure, so caught up that he didn't notice as Dave grew a second head, right beside the first. It was only as the two tongues from that head began to plunge into his ear that he finally caught on, but he could only moan as the two tongues wound around his head and down his ear canal.
"Good boy," whispered one head. "You're doing so well," said the other. Four pairs of eyes blinked at him, watching their precious little fucktoy be assaulted by their incredible body.
The two heads groaned in sync as the doubling continued, this time in their height. Dave's body and all his appendages stretched out larger and larger, doubling his height until the massive man stood 13'2, with four times the muscle mass he used to have. For Nate, it was like being in a hairy, stony cocoon, entrapped by four tree trunk arms, with four tentacle tongues twice the length of his body assaulting him from all angles. Within his ass, both of Dave's cocks grew to a staggering 20" of thick, throbbing meat, pounding Nate's tiny insides to their limits. He began to cry out, though they were quickly stifled by one of Dave's heads kissing him on the mouth. The two long tongues stuffed themselves down his throat, and a quick exploration into Dave's mouth revealed two sets of teeth, like a shark.
Dave suddenly stood up, taking the tiny boy with him as his ass began to extend out into another, muscular torso and legs, complete with four arms and two cocks between his hind legs. Wedging the sofa beneath his humantaur body, he began to hump into the cushions, while pounding harder and harder into Nate.
The poor boy screamed as his body was abused, each entry feeling like his body was being ripped in half. With a roar twice as deep, Dave arched his back for the oncoming orgasm. With four balls for each set of legs, a veritable torrent of cum flowed from his cocks, spraying all over the floor, and deep inside Nate. So strong was the flow that it began to bubble out his nose and mouth. Finally, the 3'3 boy was released from his monstrous boyfriend, and he staggered to the floor, stuffed so full of cum he could be mistaken for a beachball.
Crawling on his hands and knees, half delirious from the fucking he'd received, he made his way over to the computer.
'Error - Copy malfunction. Autosaving: every second. End output?'
He clicked yes, and finally, the transformation ended. Then, he saw the autosave function. It had saved Dave's current form as default, and wouldn't let him change it. His boyfriend was permanently a monster.