A person could always do what this game does, and just take a whole lot of screencaps of 3DCG models, cut them to pieces, and build moving paperdolls out of them. You'd need to do a lot of stretching and transforms of 2D sprites in game engine, so if a person wasn't using Godot or something it'd take some math expertise. It'd also a whole lot of fiddling to get it not to look like ass, but it's doable with basic Photoshop skills in lieu of any actual artistic talent. I ought to say that it looks like that's what was done in Slave Matrix, but I dunno if that's actually what he did. Probably the readme has some hints if you look at the credits. There'd be an awful lot of wheel-reinventing to do if a person was to clone this game; I have to wonder how long the guy behind it spent working on it. (Interestingly, PoP has the exact opposite problem, being made by an artist. Illustrating all the hybrids is the easy part for that guy.)
It's probably best to literally play it as a stock market game while you still have debt, and skip the touching game by resting. That gets you out of debt in the least amount of real time, because the actual touching game takes up a lot of time. Save a few girls you like for breeding later, and consider impregnating high-value races (once you have them) for the free girls to sell at no cost. If you're careful, you can impregnate a virgin without breaking her hymen. Once you're out of debt you can play the market some more for cash to start the breeding game. There are problems with this approach, naturally. Touching girls does increase their value, although it's slow. You don't build up your trainer skill, either, but you can always just do that once you're out of debt. Eventually, though, you'll hit on some high-value girl at a good bargain and huge chunks of debt will slough off. You'll also want to get basically familiar with what is and isn't a good price for the races--you don't have to be at all obsessive about that, but it's helpful to have a guideline in your head like "buy if under $1 mil and not scarred" or whatever. You can look at your girls' sell screens before you go to the office to get an idea of what the races you own, at least, have for a value multiplier for that day.
I don't have any idea how the mechanics for it work, but my guess is that it's due to a mutation. The manual mentions that they happen and are related to that MagCon stat. I don't know if each race has a certain percentage chance for certain mutations or weird phenotypes or what, and the things that can vary in a race after breeding seem to be pretty different from how a race can vary when generated in the shop or as parents.