Yeah, it's rare for it to be used in a way that isn't weird or forced, or in a positive way. But, I have seen 5 others where it's included and not that bad.
1. Death March in Another World Rhapsody
he saves a group of abused demihuman slaves in a country where demihumans have no rights, and they travel to find a country where they can be free. They're basically his adopted kids, and the only reason they don't remove the mark is because pretending to be his property keeps them safer.
2. Skeleton Knight From Another World
The MC actively works to shut down the slave trade, instead of owning any, and frees tons of captured elves along the way.
3. How Not to Summon a Demon Lord
The 2 girls get slave collars by accident, and a large part of the story is trying to remove the collars. It's mostly an ecchi comedy, so the author made the scenario very non-serious.
4. Rising of the Shield Hero (at first)
He is literally forced to buy a slave, even though he hates the idea, because he is betrayed and left for dead. Later on, it is less justified once they build up trust, but it works decently well at the start.
Shield Hero actually has the same problem as Death March: being Naofumi's property grants Raphtalia legal protection in a country where demihumans are considered second-class citizens at the time of his arrival
