@chojinra
This is gonna be hard to argue, as I'm not at all behind it; but there are big chunk of the world that just think that
slavery is a fantasy concept.
To that chunk, slavery is just as fantastical and foreign of a concept as sorcery, alchemy, and dragons.
I'm not singling out the author or just Japan, you can find people in many parts of the world who don't find fringe in these fantasy-slaveries, because they are so foreign,
I'm not justifying, I'm just pointing out that these fantasy-slavery is not like our slavery and shouldn't treated as is. They are as far apart as naruto and historical ninjas.
If the rule of this world is that slavery is a
magic skill which slavers can use to manipulate royal princesses and war orphans for profit, then they are so.