She was a child that was part of the "Anti-K'" project conducted by NESTS and had the power to control ice. However, her abilities were deemed to be lacking and she was marked as a defective experiment. She first met Nameless in the infirmary after he had suffered severe injuries in a mock battle to assess combat data. Meeting him greatly improved her impaired capabilities and thus she was allowed to see him again on a regular basis to nurture her powers.
Isolde eventually died during her tests and her essence was infused into the glove Nameless wears to help control his flames. Once Nameless learns of this, he works for NESTS with the hope of one day restoring her to her original body.