Mary could hardly believe his new cock. Even after the mindblowing orgasm, he couldn't wrap his mind around it. These vials were amazing. Being a male was such a different experience. He felt so powerful. And the sex drive...What felt like the equivalent of years of sexual tension was hitting him all at once. Jacking off had only been a temporary solution but he needed something more. Something to really test that new organ. But he couldn't bring himself to find a stranger and his boyfriend didn't need to know about this new development quite yet. However, Duchess was in the house....
His dog, a female Labrador, was still in his bedroom. He felt terrible, really, but these urges were too much. Quickly finding the green dog vial, Mary chugged the potion and raced up to his bedroom before the changes started. Hopefully the potions stacked and he didn't find himself turning into a bitch...
Halfway up the stairs, the naked man felt that intense heat wash over his body. Sweating, Mary was determined to get up the stairs before he lost the use of his hands. Luckily, right as that blinding pain hit, he reached up to open his bedroom door, Duchess already barking and whining to see what was the matter. The golden lab watched and sniffed in confusion as the man who smelled similar to her owner began to shrink and crunch and change.
Mary was blind to the presence of he dog as she watched deep black fur take over his arms and chest. His fingers shortened and spread while his hand swelled to amazing proportions. Thick, rough pads appeared on his palm and fingers as they continued reshaping themselves into paws. Mary could see his nose starting to stretch out, a muzzle becoming very noticeable and large in his field of vision. There was no stopping the transformation now. He reached up with his mutated appendages to feel the big, square muzzle, it was huge. His ears on top of his ears now flopped down the sides of his head but he was not shrinking much now at all. Now laying on his side, Mary watched as his dick began to erect. Whether from the transformation or the arousal of his new bestial form was unknown but this erection was different from just minutes before. His phallus kept rising until it rested on his belly. His foreskin began to thicken and his head began to change color. His penis, still human in design became a deep red color and slickened. It wasn't long until it became pointed and canine. His foreskin developed into a black, fuzzy sheath and his balls followed suit. The head of his penis retracted into it's new home as Mary watched closely. He wanted that to come out and play...But he wasn't done yet.
Limbs cracked and his chest barreled out. Gone were the pecs and instead a round, muscled rib cage became more evident. The final change to take place was the large tail that immediately started wagging the moment it grew. There on the floor of the hallway was a fully grown, jet black Great Dane.
Getting up carefully, Mary first acknowledged the height difference between himself and Duchess. He was enormous, easily taller than he was even as a human man. But the smells and the instincts. That was right...But first, Mary trotted past her whining down into her bedroom to see what she had become. In his full body mirror, he stared at the gigantic black dog looking back at him with big brown eyes. Mary gave a hefty bark, startling himself and the confused Duchess with the sheer volume and strength of his new vocal ability. His long tail wagged excitedly as he walked with grace and power. His paws were so sure and wide. He felt he could run a marathon with just a few long strides. The sheath hanging underneath his slender yet strong body caught his attention immediately. He he wished he good feel the strange new anatomy but his paws were less than sensitive compared to his human hands. The way it dangled and swayed...With all the attention his dick was getting, the deep red dick began to peek out the top. As he let his long tongue hang out as he panted, his prick bounced excitedly with each breath. He was getting aroused very fast. Soon, the red pointed rod crawled up Mary's belly before the weight made it hang down. It was so long. Mary wasn't even sure where it all came from but the red, veiny contrast was so apparent in contrast to the jet black fur on his body. His attention, however, was turned quickly to the high pitched whining at the door way, causing his dick to quickly slide back into his sheath.
With his new sense of smell, Mary could smell the bitch in heat just at the door way. This had been going on for days but before just a few moments ago, she never once gave it a second thought. Duchess was going crazy with whines and whimpers as she struggled with the idea of mating with her previous owner, even if she didn't look or smell like her owner. Mary could help her with that decision though. Quickly crossing the room with long steps, Mary gave another bark, nuzzling and nipping the female to get up. Her large hanging sheath swayed with every movement, the new sensation and hormones causing the slick red tip to emerge. Duchess's ears perked up, tail wagging and she popped up eagerly smelling the strong male scent. She gave a few smaller barks and turned around, presenting her waiting sex nice and high for the great dane.
The larger dog hopped up, resting his upper body on the bitch's back. Even with the size and height difference, she was easy to mount. With unpracticed gusto, Mary began humping Duchess. With both no experience being male or a dog, her thrusts were far from accurate. The tip of his penis emerged once more as he thrust his pelvis into the dog. Duchess stayed still as a dog, panting from the excitement already. Finally, Mary made contact with his target and the rest of his dog cock began slithering into the labrador. Once he was in, he could feel the full length of his enormous dick snaking his way into Duchess's canals. His thrusts became extremely fast and sporadic. He was so close to hitting that orgasm. Mary let out many bestial grunts and huffs feeling the rush of real male sex and something about putting the dog in doggy style. With another push, Mary could feel the knot push through into Duchess's body. More blood rushed into his highly sensitive cock and he could feel the walls of her sex clench and close around the base of his knot. The humping accelerated for just a few minutes more and Mary gave excited barks as he approached climax. Then, finally, he felt an orgasm thousands of times more sensual than his human masturbating session. Semen shot through his canine penis and fulfilled Duchess's primal desire. Mary howled and panted gave several grunts as seed passed into his dog. Of course, he had expected to pull out, as was the typical practice for any sex...But he couldn't move back off the female. His cock was being held in place by her clenched muscles around that stupid knot.
However, Duchess knew how to reacted and began twisted to get out from underneath Mary and although clumsy, Mary lifted her clumsy limbs to step over Duchess, turning them tail to tail and yet still somehow they were still tied. Looking down at himself, he could literally see his dick bending completely in the opposite direction. His member was so flexible...
They stayed tied for about 11 minutes before Mary could pull out with a wet 'pop'.