Brian slid off Mike's back as they entered the stable and pulled the doors closed. It was dark inside, but enough moon and starlight came through the various windows that he could see pretty well. He could feel the energy of the stable's magic and realized with a thrill that he could channel it as his own as long as he was inside. That was how the original stable boy had managed to do so much.
The centaur shuffled impatiently, already aroused and anxious. All that sexual desire would help any changes that Brian wanted to make - Mike was so primed to be a horse that it was almost surprising he didn't spontaneously transform all by himself. Mike looked around. "Which one should I do first?" With the enhancements Brian had already made to his sex drive, there was no question that he would be able to service both mares, and probably others, without any trouble at all.
Brian went into the stall he and Mike had shared earlier in the day and found the grooming kit the original stable boy had left there. Mike was shivering with desire, enough so that he did not notice Brian's own trembling. "I want them so bad! And I can smell them! I think they are in heat!"
"Could be." Brian sorted through the brushes until he found one that felt right. "It would take a stallion's nose to be sure. Scent is really important to horses. You won't experience sex anywhere near as intensely with that human nose." He hesitated. "I can fix that."
"Give me a horse's nose?" Mike sounded interested, if a little cautious. Well, cautious was hardly a word that applied to Mike.
Brian nodded. "I figured out a lot of the magic stuff here. How'd you like to mount them as a Clydesdale stallion, like the big horses in the beer commercials?" He grinned. "It would focus your whole body. I can use the sexual drive you're feeling right now and make it even more powerful, total lust and instinct like nothing you have ever experienced before." He could see that the idea appealed to the centaur. Part of him noticed that Mike was now more 'the centaur' than someone he thought of as his friend. That provided less distractions to his mind.
"A Clyde?" The centaur was breathing hard. "I think they're beautiful, but I don't know if I could take more intensity."
Brian moved next to him and laid a hand on the sweaty human belly, feeling the raw desire and need as a tangible force. "Trust me. You'll never regret this. Picture the most perfect Clydesdale stallion you ever saw. Think of being that stallion. With those mares!"
The centaur got a faraway look in his eyes, and Brian could sense the energies focus even more. Dragging a wooden bucket around in front of the dazed creature, Brian climbed up and started stroking Mike's cheeks. The human features distorted rapidly, swelling out into an equine muzzle. "You are a magnificent Clydesdale, a stallion, a champion stud. Feel the need. Let your desires shape you."
Power seemed to surge through Brian and he gasped as his own face started to push outward! Concentrating hard, he dropped the brush and placed his hands on the centaur's forming muzzle. Then he willed the transformation energy out, sending it into the very equine head in his hands. Brian felt his own features return to human as the centaur's head completely altered to that of a Clydesdale. With the flow established, he simply stood there with his fingers splayed over the massive cheeks and let the magic work. The centaur's shoulders drooped, and his arms shrank away. Brian slid his hands up to frame the magnificent animal eyes as the centaur's head dropped lower. His human chest was fully furred, and as the last bumps of his shoulders melted away, became the horse's neck.
Brian shuddered as he felt the centaur's mind succumb to animal instincts, and stroked the protruding brows as he used the magic to slide in with the instincts. This was how he could make this permanent. Brian touched memories, knowledge, skills that belonged to the centaur, and the human he had been before. Very carefully, very gently, he added new memories and skills, the life of a horse, the skills of a pack animal, the instincts of a stallion. And as he added those, he took away far more. He was replacing 18 years of human life with 3 years of horse existence, removing and erasing instead of altering. That was what would make the difference. By removing humanity instead of transforming it, there would be nothing to restore.
Best of all, the centaur helped him, wanted it, accepted the new identity with enthusiasm. At first he was simply choosing the sexual experience, but then he was the Clydesdale. The animal trembled still, but when the magical energies finally faded he was a horse. Brian sagged, exhausted and feeling incredibly satisfied, but he made himself lead the prancing, snorting stallion to the stall where a female Clydesdale was quartered. It took no urging at all to get the male inside, and he shut the gate with a sigh of relief. No doubt the others would come looking for them in the morning. Mike was no longer recognizable to anyone. Brian would have to see what he could about his own appearance.