Eventually, the visiting canine reached his limit and climaxed with a howl. The cry was joined along with Fang's sharp yelp as she too peaked, spraying newly feminine fluids onto the mounted male's groin. The two remained joined for a time. Fang kneeling underneath the intruding male still straddling the Newfoundland. The two dogs stayed like this, panting heavily until the mysterious male hound pulled out with a lewd, moist pop. He sniffed at his mate's rear a few times before losing interest and walking off, presumably back to its own yard, leaving Fang and her former master alone.
As Jeff's host lay on her flank, panting as she lifted a hind leg and commenced cleaning her newly acquired vulva, he could think about how glad he was to have made it through that ordeal. He felt as though someone had repeatedly kicked him in the balls. The next chance he got, if one even arose, he would definitely need to make some further adjustments to his living arrangements. For now, Jeff resigned himself to his fate, his pink, puckered formed twitched and shuddered under his dog's tail while she licked herself. Jeff paused.
"Her." He thought. Jeff had transformed his family's Newfoundland dog, previously male, into a female. The dog's penis, which Jeff not long ago served as had been fully repurposed as part of a tight, puffy vulva becoming the clitoris while the dog's testicles had been reconfigured into functioning ovaries. Female hormones inundated the canine's body as its very genetic code was rewritten as that of a female Newfoundland dog. Fang's mind warped as her demeanor became much more subdued and maternal. Her memories were remembered from the point of view of a Newfoundland bitch. The simple dog had not noticed her metamorphosis and as far as it and the universe were concerned this was the way things had always been.
Of course, this did little to alter Jeff's plight. Whether Fang was now a female or not, he was still his dog's digestive tract with his face now serving as her pink anus. Jeff was not sure how much time had passed since they slept, but he had been part of his dog in one way or form for a full day. His eight-hour window had come and gone, leaving stuck in his current form for good. His situation could only be manually reset after a full twenty-four hours elapsed from the last transformation, but Jeff would not be in any shape to initiate such a reset. Even if he could somehow miraculously communicate with someone and get them to enact the changes for him he could never again be restored to human form. He'd only be able to change into whatever was close by. The best-case scenario to being human once more was for Fang to be near another human at the opportune time at which point Jeff could have chosen to become part of that person. That was it though, he'd never be able to do much better than that at this point. Even that was a pipe dream at best since he could not initialize the manual reset anyway.
No, Jeff was screwed. He knew that, barring some miraculous fluke, he would remain as Fang's sentient anus for the rest of his existence. All because he had to tamper with things no mortal should be entrusted with. His hopes and dreams. Ambitions. All were rendered moot as his only purpose in life now was to serve as the endpoint of his dog's digestive tract. Expelling her gas and waste.
Jeff was brought out of his thoughts as Fang began to move. He was so lost in his own mind that Jeff did not notice that his dog had finished cleaning and ready to move on. The large, black pooch rolled to her feet and stretched out her legs, pointing her rear up into the air when she flexed her hindlegs. Panting happily Fang rested on her haunches as she recalled not seeing one of her human companions for some time. The smaller adolescent male that lived with her. The one that always played with her around this time. She looked around, sniffing the air before grunting as a brassy bout of gas erupted from her rear and she found herself no longer thinking of her human playmate. Instead, the Newfoundland padded off towards the shade of a tree where one of her favorite chew toys laid waiting, totally unaware of the fate that had befallen Jeff.