@dkdumpling I'm more amused by the very idea of the slaves in the first place. As I was replying in agreement to the person before me, slaves in a lot of these stories are just glorified pets with a different name. A way for the protagonist to essentially own a heroine in all but the cruelest of meanings because they water down the freedoms of the owners to the point if you slightly touched the person you apparently own inappropriately, the royal guard might bust your ribs. Why even be slaves in the first place? It's just a weird system to bring into a story when there's almost no reason to. There's a hundred circumstances that could have yielded a similar tone than finding the broken slave girl and fixing her. The author just wants him to be her master at the end of the day. But it's okay guys, he's not paying into a really messed up system or anything, okay?
As far as this story goes, he hadn't even found the broken girl until after he already expressed interest in owning a slave. Finding the girl only made the "obvious" decision easier at the end, but had there not been a really messed up girl I don't doubt for a minute he wouldn't have picked someone else. This world allowed slavery, and it piqued his interest.