Jake grinded himself slightly against the chair, feeling the smooth blank space where his balls had once been. He was going to make his 'master' pay for neutering him all those years ago. Selecting special options on the program, he dragged both their wireframe models together, chuckling to himself wickedly as he set his cruel new change to permanent. He turned, looking over at Mike, who was totally lost in the pleasure of stroking and squeezing his twitching new dog dick.
"Enjoy that while you can, boy."
Jake jumped down from the chair then up onto the bed, watching as Mike began to paw at his clothes, pushing them off and whining as his thrusting, humping masturbation became more desperate. All the human could think about was sex and fucking, half mad with lust. Mike's skin began to feel strange and sensitive, small bumps rising on him all over. Bit by bit, his hair fell out, falling in clumps to the ground as his body hair also fell away, soon leaving him smooth and pink all over. Next to follow were his fingernails and toenails, and his stomach gurgled strangely as his internal organs began to change, becoming an indistinct mass of flesh. He did not notice anything, too busy stroking and squeezing his fat new dog dick, until one by one his teeth fell out. Only then did he sit upright, realizing to his horror that his heart had stopped beating. His skin, tingling and bizarrely erotic to the touch, had now begun to sprout a few spare, short black hairs, though it was hair that looked nothing like what Mike had once had.
He felt something shifting in his bones, and flopped limply back onto the bed, his skeleton softening and merging into the rest of his body. Limply, he deflated slightly, looking like nothing more than a big sack of human-shaped flesh. Jake walked up over him, raising one rear leg and showing off the small pink scar where the dog's balls had once been. With a sinister canine grin, Jake lowered himself down so that the scar was touching Mike's still-erect canine cock. Mike shuddered, moaning as his dick began to soften, the flesh fusing and melting into Jake's crotch as he felt himself being pulled up.
A new heartbeat began to push through Mike's body, the beat of Jake's heart as the dog's blood flowed into him, sustaining him. His legs melted together, fusing into one lump as his arms pressed against his sides and also began to disappear, pulled into his torso. Mike groaned, feeling his cock and balls merge into the flesh at his changing crotch, though he could still feel his package as a sort of hard lump inside him, which began to grow and cause the lower half of his body to hang down from Jake's crotch. His head began to sink into the sack of flesh that was now his body, which was rapidly shrinking and drawing up against Jake's crotch, hanging there as a part of the dog's own body. The last view of the outside world that Mike got was looking up at Jake's panting face staring down at him, before his vision was sucked into the pulsing wet darkness of the inside of his dog's ballsack. He hung there, just a pair of inanimate balls in the warm darkness, until he felt his former cock and balls begin to ooze thick white semen, which also flowed freely from what was once his head. Outside, Jake had bent over, and was beginning to lick his proud, newly-restored testicles, sending a shivering pleasure through Mike's body. Mike could only taste and smell the dog cum all around him, trapped forever as his former pet's reproductive organs.