Neifirst was the result of an accident in the Biosystems Lab on Motavia in AW 1282; she was the first numan (a hybrid of biomonsters and humans). Shortly after her "birth," she turned on her creators (who wanted to kill her) and caused a massive biomonster outbreak to begin on Motavia. On August 30, AW 1283, Nei split from Neifirst and ran away from the lab and went to Paseo, where she was taken in by Rolf Landale
The next year, in AW 1284, the two "sisters" confronted each other again at Climatrol Nei attacks Neifirst alone, before the others can intervene. Ultimately, the defeat of Neifirst ends in tragedy as Nei dies with her; because Nei is a splinter off of Neifirst's "whole", Neifirst can exist without Nei (as shown when Nei dies in battle and is able to be restored at the Clone Labs in normal play), but if Neifirst perishes, Nei can no longer exist.
Neifirst is found in the middle of Climatrol's eighth floor. She has 1,100 hit points, an attack power of 178 and a defense power of 10. Defeating her earns the characters 1,1111 experience and 1,111 Meseta.