A race has slave ancestry as a defining element of their culture.
At some point in the past, one group of people enslaved another, and that enslaved group later regained their freedom. But their years as slaves have left a mark even on their free descendants, who aren't about to forget what was done to them any time soon. As a possible part of a race's hat, or a facet of broader character development, Sons of Slaves have a higher likelihood of exhibiting a number of certain tropes. They may place a high value on things that belong to their traditional culture, especially if that culture is in danger of being lost otherwise, and put greater stock in group unity. Bonus points if that culture takes inspiration from Magical Negro and/or Magical Native American tropes. They have a higher-than-average chance of spawning ProudWarriorRaceGuys, especially if they bear a grudge against their former captors. And if Slave Liberation or a similar cause figures in a plot, expect them to be deeply enmeshed in it.