 Justine's exact origins are unknown, but it is known that Bianca once wanted her as one of her prostitutes, and that Thomas saved her from such a fate.She became his lover and food source, regularly having sex to sustain him at the cost of her own life force.This was especially necessary since Justine lacks the emotional and mental control that most humans have, and experiences wild manic mood swings when Thomas is not nearby to sap away those emotions.