marshmallowcreampie
If slavery exists in some part of your story, just use it to show how EVUL a character is by him having slaves. Because in all settings, slaves are the workers of choice for villains! It's not like slave owners live in fear of rebellions and only have slaves because economic conditions like the work being too dangerous or grueling pressure them to do it! And when your hero wants to free the slaves, all they have to do is give a rousing speech! After all, it's not like there are physical or psychological reasons that keep them there! Slaves never rebel on their own, but once your hero comes in and tells them they should be free, they're totally for it!
emotion_awesome
No one owns slaves and:
Does so because they'd lose their wealth/land/business contacts without using slaves
Does their best to get along with slaves
Gives slaves medicine
Calls a doctor for slaves
Gives a slave a wedding gift
Allows a slave to learn anything
Has a slave's child be a friend for their own child
Lets a slave buy freedom
Uses current slaves as a cover or helpers to free other slaves