Once they were inside, Brian hopped down and carefully closed the stable doors. They had made it all the way without anyone seeing or hearing them, or at least without anyone raising an alarm. Brian suspected that would change if they tried to leave - after all, the townspeople wanted centaurs to come into the stable.
Mike was already staring at the beautiful black Shire mare. She was bigger than he was, a mature animal where he was still a young stallion in the horse parts. But she was also in heat, and even Brian could smell her need. Mike was coming erect in response and took a few steps towards her large stall. Then he looked over at Brian. "You think it's safe to mount her without the wizard here?"
Brian grinned and moved to stand at Mike's rump. He slid his fingers over the taught orbs of Mike's black testicles, enhancing his friend's desire. "The wizard won't be here to do anything to you at all. You should take advantage of the opportunity. She wants you right now."
Mike was only partly aware of Brian's gentle rubbing, and while he suspected it was making him even hornier, the desire to mount the mare was already powerful. His shaft was fully erect now, arching stiffly under his belly. Brian moved beside him, sliding a palm down Mike's equine side. He stopped and grinned up at Mike, who was trembling as he stood there. "Scared?"
"A little." Mike admitted. "She's really big. And what happens if the wizard comes in?"
"Even if the wizard did see you, he wanted you to mount the mare anyway. So you'll be doing what he wants."
Mike frowned. "Yeah. he wants me to mount her. Maybe because that will make me change?"
Uh-oh. Brian moves quickly to open the mare's stall gate and stepped inside. She had squatted and urinated, and now her tail was flagged to the side and her black lips clenched and unclenched, winking at her stallion. He slid his fingers over the slick folds and then went back outside to Mike. "Here! Smell this." He held up his wet hands, and as Mike leaned down slightly, pushed his fingers into his friend's nostrils.
Mike jerked his head back. "Hey!" He wiped at the slick mare's fluids, but then dropped his hand and shivered as her scent broke his last restraint. shuffling forward, he started breathing deeply, eyes wide. His human mind was becoming overwhelmed by stallion's instincts. There was no real contest. Mike had wanted to mount mares before they even got here. With the centaur inside the stable he would not have been able to resist even if he'd been brought here by force.
Even though he was expecting it, Brian was startled by the sudden leap and thrust. Mike pushed up over the mare's rump, rocking back and forth a couple of times as his cock missed the opening, and then shoving forward with a grunt as he drove in.
It was fascinating to watch the animals mate. The mare braced herself and hung her head low, while Mike pounded her brutally. His muscles rippled with each stroke, and Brian realized the centaur was getting larger, more mature. His human features shifted from late tweens to early twenties, then thirty, and his body thickened and got hairier. By the time Mike shuddered in release, he was a mature centaur, the equivalent of a ten year-old Shire. Both he and the mare cried out in pleasure, and then he slid off slowly and stood beside her, sweating and panting.
"Oh, wow." Mike's voice was much deeper, but he did not seem to notice. His face protruded out some, and his eyes were large and almost solid brown, like a horse's. His body hair was black, and thick enough to almost cover the skin of his human torso and arms.
Brian came into the stall and hugged Mike's equine chest, not minding the sweat. If things were working right, more than Mike's body was changing. Mixed in with his human memories were new memories of being a horse, years of training and experience as a beast of burden beginning to take shape. His friend would not even be aware of the slow shift of thoughts, accepting the equine mindset as something natural and normal. He just needed Mike to mount the mare one more time.