Nothing you can't handle

The very first centaur takes a lot. You have to figure out a great many details no one would normally have to think about. Even the way the digestive system connects isn't obvious - since horses can eat grasses and humans normally do not. But you do manage to create something that's more than the sum of its parts. A few problems here and there, like a slightly lower top speed, made up for by many advantages, like the fact centaurs will be able to eat human foods for extra energy but can still survive off vegetables and grasses if they have to. They also won't have to chew up all those greens, something they couldn't do with a human's smaller jaws, nor do they have to chew their cud, something you're sure would hurt their popularity. Instead you supercharged their stomachs and intestines, so they can gorge themselves and then digest as they walk, pumping grass between the lobes of their stomachs instead of back up their throats.

For your first 'contestant' you made sure to choose a man who was short, not only in his height but also in terms of his manhood. Navir wasn't exactly willing, but he was resigned to his fate. You made the transformation as painless as possible and, hoping to win some points with him, you made sure to bond him to a large, strong stallion with an equally large package. When he realized that it wouldn't be agonizingly painful, his mood improved. When he realized just how strong he felt and how he could literally look down on other people now, his mood improved even more. When he craned his neck and upper body to get a good look at his new foot and a quarter long cock, three inches across, big balls below... well, suddenly he was smiling all the time.

Not that you're planning to tell him, but you did make some minor adjustments to the horse's cock shape and size. It was actually even bigger before. In exchange you strengthened some important muscles and made it look a lot more human than the real thing. Just enough to make it distinctly different from either human or horse - mainly so it won't flop around in the breeze when he's aroused. If he finds a willing centauress those stronger muscles will also make the aiming process a lot simpler.

For the most part you kept the human half as human as possible. That's what centaurs are supposed to look like after all. You have to fight with the natural impulses of the spells you're using, which try to change fingers for hooves and attempt to stretch most of the face into a long muzzle.

When you bring him out to show him off he's still unsteady on his feet, but grinning from ear to ear. The looks of some of the women in the crowd make you reconsider the 'willing centauress' part - a few of these women are doing a poor job of hiding how interested they are by what they're seeing. Navir knows too - and he winks whenever he catches one looking at him. Having a fifteen inch cock is a hell of a confidence boost, even if you need to gain hooves and learn to walk again as part of the bargain.

You thought you'd chosen a good first contestant, but it turns out he was downright ideal. Navir is quite happy to put on shows as soon as he's comfortable. It's obvious that his relationship with Andreas, the man chosen as his rider, is excellent - the two of them could have been drinking buddies in another life the way they get on. Master, servant, rider, centaur, noble, **** - within a week none of that really seems to matter, at least to them.

As expected, creating a centaur pisses a lot of people off. There are complaints from the church, as expected, as well as from nobles who think this is going too far. And there's one person at your home who's more furious than most. Doe had the chance to get a look at Navir after his transformation. She has all kinds of creative names for you, the king, the people and even for Navir himself since he's now going along with it. She paces in her 'guest room', seeming to live off malice and hate.

As the days go by...

You get better and better with each new pair. At first you stick to changing men into centaurs, mainly due to the number of stallions in the army. Not everyone is as happy about their new life as Navir, but you do see several matchups of riders and new steeds that look promising. One pairing of a fiery young man, a shiny black coated beauty of a horse and an expert lady of the cavalry famous for breaking horses from a very young age makes you and several other people laugh. Immediately there's a betting pool for how long it will take her to bring him to heel.

On the seventh day you finally decide to tackle the distaff side of things. A lot of additional thought is needed - women and men do have some serious differences when it gets down to something as delicate as combining two different species. Plus you want to make sure the centauresses are 'well sized' as one drunken noble put it while he was idly speculating on the subject of the female captives. As in, they need to have a deep enough vagina to comfortably take a centaur's shaft, but a tight enough one to please a human. You've got no doubt that just as thirsty women are looking for some alone time with a centaur the centauresses will prove equally popular with men. Hmmm... perhaps you can do some things to guarantee it.

Centaurs are supposed to be horny devils. The men you transformed didn't need any help with that, but you decide to give the centauresses a tight pussy with an even more human appearance and above human sensitivity. Even a clumsy lover should be able to make them happy, especially since they'll have more trouble pleasuring themselves. As an added bonus, since centauresses are going to have to feed bigger babies you decide to add a little to their chest. Thanks to the size of their abdomen these women will get something of an hourglass shape for free.

Your first centauress, Lillian, proves to be a big hit. A bit resigned to her fate, she's unsure about the whole process. Then her new master brushes down her soft black coat. You hadn't really intended for that to be quite as nice as it obviously is for her, but it looks like there's a reason normal horses enjoy it. You chalk this up as one more incentive for the girls - or perhaps the male centaurs enjoy it just as much as the centauresses but hide it? Who knows.

It's only after Lillian gets led away, passive and leaning against her new owner, that Doe ends up talking to you again. You did let her out for dinner, but she barely spoke to you. This time she eats most of her food in silence, as usual, then stares at you. "I guess sooner or later you're doing that to me."

Ah perfect, this is the opportunity you've been waiting for.