Neifirst is the first enemy boss character from Phantasy Star II. She is revealed to be the "sister" counterpart to Nei.
According to scientists, Nefirst was the first result of a product of a mixture of both biomonster and human. However, she was deemed a "failed" experiment and was placed on bounty, in which she was nearly killed. The betrayal soon provoked her to anger and hatred; for her revenge, she raided the Biosystems Lab and the Climate Control, stealing DNA and power from both facilities, therefore gaining control. It was there that she was also able to manipulate the laboratory into producing a massive number of biomonsters and released them on a raid on Motavia for revenge against those who opposed and feared her, thus, setting up the events of Phantasy Star II. By this time, however, another result of the same creation rebelled against the tirade (that being, itself, manifested to be called Nei), and both were completely separated.
Neifirst would later be discovered by a government agent named Rolf and his companions after their arrival of the climate control. She revealed that both hers' and Nei's origins are the same; they are both the result of the completed experiment, each part of one another, and because of this, both became outcasts from society; she also told that Nei cannot survive without her, as both and their lives are physically and mentally connected. She tries to coerce the latter into saying that her name represents "evil" and live by it, but Nei claims that she left her other part both because of the dangers of revenge and did not want to make any of the problem more worst. Neifirst is angered by this and makes her chose to either fight her or leave immediately. The two numans engage into a duel, where Neifirst manages to gain an upper hand on her opponent and defeat her, killing her in process. However, afterwards, she is defeated by Rolf and his comrades, leaving both "sisters" dead and thus ending the biomonster hazard. But because Neifirst was no longer alive, the climate control went berserk and exploded.
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