Naida comes from money—she's the daughter of a wealthy aristocrat on Planet Fleed, which is how she crossed paths with Duke Fleed in the first place. They grew up together as childhood friends.
Things took a dark turn when she got brainwashed using some kind of device designed to mess with her head. The whole point was to turn her into a weapon against Duke, forcing her to psychologically torment him and ultimately kill him. It's a pretty brutal setup, and fans often note it as one of the series' darker plot turns involving someone close to the protagonist.
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