She's just a child and not a loli! Not even a slave, since she wasn't bought or sold, just captured! It may be semantics, but I believe its more to depict how rotten some humans can be! Something to weight on the MC
If it's basically just a brand that doesn't have any real magical properties, couldn't he just heal it? I mean, at the end of the day a brand is really just a patterned burn scar.