Cordelia Glauca operates as a core member of the Milky Holmes detective unit, embracing a self-imposed role as the group's eldest sister figure. This persona fuels overprotective tendencies toward her teammates and triggers elaborate delusional interpretations of their relationships, often fixating on maintaining group harmony. Her artistic hobby involves persistent drawing sessions depicting Milky Holmes members together in flower fields, though these works display limited technical skill. Flowers consistently inspire her expressions, and she intermittently breaks into spontaneous song during ordinary conversation without clear intent.

Profound fears dominate her reactions, specifically an intense phobia of dark enclosed spaces and sea cucumbers. Exposure to darkness induces severe psychological distress, eroding emotional control and unleashing monstrous physical strength that destroys nearby objects indiscriminately. This altered state also manifests perverted behavior, evidenced when she forcibly stripped teammate Hercule Burton's clothing during a confinement incident.

Her supernatural Toy ability grants heightened sensory perception, enabling her to see, hear, and smell beyond human limits to detect imperceptible details. This power once allowed her to track combatant Stone River's movements and dismantle Lady Arsene's complex illusions. However, Cordelia and her teammates lose their Toys early in the narrative after an encounter with the Thieves' Empire, rendering this ability largely inaccessible.

Under duress, she exhibits exceptional reflexes—such as deflecting sword strikes with improvised defenses. Extreme despair unconsciously triggers her projection of hypnotic flower-field imagery onto others. As a British detective student at Yokohama's Holmes Detective Academy, she participates in school activities and investigations to reclaim the Milky Holmes unit's lost Toys after their defeat by the Gentleman Thieves, including missions to thwart Henriette Mystère at a museum.