Mike thought a moment and then said "I guess the biggest single change would be my soul. Once that's done, the rest should be easier to accept."
The Wizard nodded. "True enough. And I think I can make the transition quite a pleasant one. Aaron, run back to the town stable and bring Nightmare back to us."
The young man blinked, and then grinned and ran out.
"Nightmare?" Mike looked a little concerned.
"A very fiery and powerful Shire mare, a true warhorse from generations back." The Wizard came over to Mike and ran his hands over the centaur's equine back, and then reached underneath to stroke the heavy black sheath. "But I promise she will be very happy to see you."
Mike blinked as warmth spread through his groin, and his equine shaft started to emerge. At the same time, pressure built in his testicles. He twisted around as much as he could and just barely got a view of his own dangling orbs. They were getting larger, heavier, the black flesh stretching out and dropping.
"Sex is more than just pleasure or reproduction. There is a direct link to your soul. The sexual connection is more who you are than anything else." The Wizard stepped back, but no further assistance was needed. Mike felt pressure and desire and warmth and need building. I have changed your sex fully into that of a Shire stallion, and the link with your soul is shadowed with the beast. When you mate with the mare, the combination of her sex and soul with your sex will be enough to let you allow your soul to change. I cannot describe the experience for I have never had it. But once done, it cannot be undone."
Mike's eyes were wide, aware of his own erection and a pulsing that started in his loins and seemed to flow up into his skull. The Wizard walked around huim, stroking his sides, his rump, even his human chest. Every touch made the sexual sensations grow stronger, the pulsing deeper.
Then he both heard and smelled Nightmare as Aaron returned. The mare was huge, a little larger than Mike's horse parts, coal black all over. She laid her ears back when she saw the centaur, but did not pull from Aaron. And her scent! Mike flushed with sudden desire, but held back until the young man let her free.
She trotted over to him and whinnied, snuffling at his human chest and face in apparent confusion. But then she moved to his equine portion and he felt her own heat intensify. Aaron slipped his fingers into her slick folds and wiped the fluids across Mike's nose and mouth. The pulsing got stronger.
Oddly, the desire was strong but not overwhelming. He could resist the urge, the need in his loins. Maybe because his soul was still... human? Centaur? But he knew that once he let go and mounted her, that would change. Regardless of his outward appearance, he would be a Shire stallion. Was he ready to give in? To make that ultimate sacrifice?