Nirrti is the elder sister to Neyla, though she often refers to Neyla as 'mother'. She is very cautious around the latter, never boarding Shadow of Prosperity, as Cynder and members of the Coalition do.
Nirrti's appearance differs dramatically from Neyla's, though both are humanoid tigers. While Neyla's fur is purple with blue stripes, Nirrti's fur is white with black stripes. Also unlike Neyla, she has a long, bushy tail (Neyla's tail is long, but not bushy). She is also able to bring almost the entire system defense fleet with her, indicating that she is of higher status then, or is entrusted with military power more then Neyla.
Nirrti shares Neyla's habit of eating those condemned by the state as traitors, though she wears more substantial clothing then Neyla does (the later is described as wearing only a lose-fitting silk robe). She also has the councilor's seal-a golden 'a' emblazoned on a silver background.
Nirrti is mentioned by Neyla after discovering that her guards had accidentally released the Koozer-Ga, and when they were killed by the parasite, they used the guard's memories to locate, and eventually attack her before she was saved by Cynder. Nirrti later appears in person when New Atlantis is attacked for the third and final time; she is refered to several times prior to this by Neyla, who states that she had contacted her during battle ragain around the outskirts of the city, which gradually movend into the downtown areas, triggering emergency defense protocols.