The relationship between Gan and T'Gatoi in Bloodchild and the relationship between Rufus and Dana in Kindred both hinge on power dynamics.
In Bloodchild, the Tlic, an alien species, have placed all the humans in a reserve and use them for child-bearing. After watching another human give birth to Tlic eggs, Gan questions whether he wants to be a host for T'Gatoi. At first, he feels grateful to T'Gatoi for protecting his home, the Preserve, but after seeing T'Gatoi help a human give birth to Tlic eggs, he grows suspicious and disgusted; he no longer trusts T'Gatoi. However, Gan doesn't have much choice in whether he hosts T'Gatoi's eggs or not, so he threatens suicide. After that, T'Gatoi and Gan come to an understanding, and Gan decides to host T'Gatoi's eggs. The societal hierarchy is maintained, and Gan lives like the other humans in the Preserve.
A large portion of Kindred takes place in the nineteenth-century American South, where black people were enslaved and treated much like the humans in Bloodchild. The white people, such as Rufus, had control over every part of their black slaves' lives. Dana is a black woman who travels back in time from the 1970s to the 1800s. Since Dana is a black woman, the racial power structure affects her when she's with Rufus. Rufus has many opportunities to turn Dana in to the authorities, taking away her autonomy and, possibly, her life.
Just as T'Gatoi has socially-granted power over Gan, so Rufus has power over Dana. Both power structures hinge on arbitrary, and unchangeable, factors: species and race.