Who is the antagonist in the novel, The Joys of Motherhood?

Nnu Ego's Chi serves as the antagonist in the novel. A "chi" is a spirit of someone who has died, a spirit that becomes the personal god of someone living. Nnu Ego's chi is the spirit of a female servant, ritually sacrificed as part of the funeral for the woman who was Agbadi's senior wife - a woman who, the narrative suggests, died after overhearing the sexual pleasure Ona and Agbadi gave each other. The servant did not go to her death willingly, which means (according to the value system in which Nnu Ego grew up) that her soul was angry. Nnu Ego believes the anger of her chi is the reason why Nnu Ego's first child died, and why she suffered to much in her life.