From Octavia Butler's excellent Xenogenesis Trilogy.

Nikanj is an ooloi (no I don't know how to pronouce it either) the third sexless member, genetic manipulator and healer of the Oankali race.

Nikanj is paired with the human Lilith Iyapo during its adolescence.Despite some initial reluctance, the two eventual become part of a whole five person (Human male and female, Oankali male and female, and oolio) mating thing and produce several hybrid children.