Mike thought a moment, then said "My body first. That way I can experience the changes with my human memories."
The Wizard nodded and smiled. "A wise choice. Aaron, use the grooming brushes in the stall - they will purify him physically into a Shire stallion. After that is done, we can do the bonding, and finish up with the mental changes. That will provide our centaur with comprehension of his transformation right up tot he point we are finished."
Aaron patted Mike's rump. "Go on into the stall."
Taking a deep breath, the centaur shuffled in. He was nervous and excited, not sure if he was being stupid, but unwilling to pass up this chance to be so totally transformed. His red-haired future master came in and pulled the gate shut, then took time to slide his hands all over Mike's equine body. The firm rubbing was pleasant and almost intimate, then became very intimate as Aaron massaged Mike's sheath and testicles. The centaur's cheeks flushed, but he did not complain. In truth, he liked it, and as a horse, he would feel no embarrassment about being handled like this.
Aaron grinned at him. "You are going to be so magnificent!" He moved to the side of the stall and picked up a large stiff-looking brush with a black handle trimmed in polished silver. "You ready?" He slipped it on his hand.
"Go on. Start with my back end so I can watch." Mike twisted around as the red-haired young man touched the brush to the centaur's left flank. At first, nothing seemed to happen. Then a curious pulling and warmth began to build as Aaron pulled the bristles across Mike's equine coat. The dark brown fur took on a shine as it darkened even more, turning a silky midnight black and lengthening. The transformation started slowly, then spread outward more quickly as Aaron worked.
"Magic is a little like starting a fire." The young Wizard explained from the other side of the gate. "You have to work to get it started, but then all you have to do is keep it fueled."
That was obvious as Mike watched - silky black horsehide was flowing across his equine rump like ink spreading from the brush. The heat was also moving inward, creating curious sensation of swelling in his muscles. His back end got lopsided, and Mike realized one leg was now thicker and longer than the other. However, his back end was soon level again as Aaron completed the changes to the right side. Mike gasped and shivered as the bristles slid lightly over his genitals, feeling testicles swell and his already huge shaft enlarge. "Oh, man. I am going to want a mare."
Aaron laughed. "You will definitely get one. Maybe more!"
Mike kept watching, amazed at how the transformation was moving along now. He could see the edge of black as it moved forward, his insides shifting and spine lengthening. Aaron was more encouraging than causing the changes now, using the brush to spread and direct the Shire form. Mike's forelegs seemed to push against the ground as they lengthened and thickened, hooves expanding under a bright white cascade of feathering. The change slowed drastically as Mike's equine parts completed the change, leaving him fully Shire stallion from the waist down. He could see the boundary between human and horseflesh creeping upward, though, and knew the magic had not stopped.
The Wizard nodded in approval. "Breed and color are simple changes. The rest of you requires more work to transform."
Mike stretched out his legs and twisted around both ways to admire his massive black form. "Wow! This feels amazing, like I could pull cars, kick down walls."
Aaron chuckled. "I do not know what a car is, but you could pull a half-dozen loaded wagons at a time. And one of your hind hooves could easily take down a stone wall." He moved around to face Mike and ran the brush down his chest and belly. "Now for the real changes."
The touch of the bristles against Mike's chest triggered a rapid spread upward of black horsehide, and also seemed to change his perspective. As Aaron ran the brush around his sides and belly, it became obvious that his human torso was starting to sink into the equine neck. He was so fascinated that his arms had dwindled to the size of a small boy's before he realized they were shrinking away. He started to comment, only to have his breath catch in his chest and his heart start to race wildly. Mike's eyes widened in fear, not quite in pain but suddenly unable to draw breath. At least not the way he had before. His ribcage collapsed in on itself, replaced by rippling muscles, and his arms flailed into sticks and finally were absorbed into a horse's neck. The pounding and shortness of breath vanished as his Shire's organs took on the full duty that had been shared with human parts before, but when he tried to speak all that came out was a neighing.
Aaron patted his neck. "Just your head now." He ran the brush over Mike's face, but the magic was already working on the former centaur's skull. Mike felt his head shift, his eyes drift apart, and his ears move as his skull became that of a Shire. Vision blurred and changed, and his face pushed out into a dark mass that split his vision. Scents grew more intense, as did sound, but colors faded and his eyesight got grainy, like a digital picture blown up too far.
Mike felt confused now, struggling with his changed form and sensations, and feeling thickness already drifting across his thoughts. Aaron continued to groom him until the Wizard opened the stall gate and came in. "That is enough. He is fully a beast physically, which will be affecting how he thinks as well. Put the brush away while I prepare for the bonding and training."