Kako Kurai enforces school regulations as the public morals officer, convinced that disorder in personal presentation reflects disorderly public conduct. She possesses short, dark gray-black hair fading to purple, cut above the shoulders with bangs, typically secured by a thin black headband featuring a small bow on the left side. Her light green eyes complement the standard school uniform and black stockings worn above her knees.

Kako adheres to a strict personal rule against forming friendships, believing self-reliance and emotional independence are paramount for becoming a strong, solitary individual. This philosophy manifests as deliberate aloofness and resistance to social advances, making her a significant challenge for Bocchi Hitori's attempts at friendship. However, Kako displays unexpected vulnerability when faced with surprising situations, revealing an internal conflict between her ideals and innate reactions.

Her specific idiosyncrasies include a particular affection for elephants and an intense fear of dogs, which sometimes influence her interactions. Her name originates from the Japanese phrase "kurai kako" (暗い過去), translating to "dark past," though the specific events or nature of this past are not detailed. Her documented character trajectory shows no significant evolution or resolution regarding her friendship policy, background exploration, or interpersonal developments across media.