Who is Mama from The Infernal Desire Machines of Doctor Hoffman: A Novel and what is their importance?

Mama is Nao-Kurai's mother. Mama helps raise the children because Nao-Kurai's wife died while giving birth to his youngest son. Mama also takes Desiderio into the home with much affection, caring for him like her own child. When Desiderio comes to Mama with questions about the marriage process, Mama begins a sexual relationship with him. Soon Desiderio finds himself with two willing lovers. It is this relationship that hurts Desiderio the most when he realizes he must leave the tribe to save his own life.