Fortunately, reputation is lost and gained. and you can easily save dozens of unwanted slaves from bandits and let them go, and keep the 21st person you like. and at the same time still remain in the plus in reputation.
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However, if you want to be Fundamentally White (which is strange, given that you play for a slave magician), you can order a couple of cows from Sebastian. And it will be fast and not very expensive.
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Personally, I am more upset that it is impossible to "increase the fluidity" of slaves - the beast of girls. I mean turn beastkin into halfkin. When breeding with most races beastkin, they lose their fur, which is sad.