her sister Neifirst, whom Nei was originally part of. She split with her because Nei didn't like Neifirst's view on humanity.
The name Nei comes from the native language, which describes her aptly: "The Human who is Not A Human". One of the many biogenetically engineered beings created by the supercomputer Mother Brain, Nei was frequently seen as a freak and was never accepted into society until a sympathetic soldier took her in. Since then, Nei has remained by his side, through thick and thin.