Cathy is a worker fairy enslaved to Jonas Anders. Her appearance reflects typical fairy traits without further elaboration. She exhibits fierce loyalty to Jonas, accompanying him on his travels, including the pursuit of Anne Halford along the hazardous bloody road. This loyalty manifests as deference toward Jonas but open disrespect toward Anne, occasionally prompting reprimands from Jonas for her behavior.

Cathy's primary narrative role involves falsely accusing Mythril Lid Pod of stealing Anne Halford's silver sugar, claiming firsthand witness to the theft. This accusation is later revealed as a fabrication; Cathy herself stole the silver sugar under Jonas's explicit orders. The theft was part of Jonas's scheme to present Anne's work as his own at the Lewiston competition. Cathy utilized her ability to become completely invisible to facilitate this sabotage.

Documented materials show no significant character development or shift in her motivations. Her actions consistently serve Jonas's directives, reinforcing her role as an instrument of his deceit. Following the exposure of the theft and Jonas's subsequent failures, Cathy's storyline continues without evolution or independent agency beyond her association with him.