Kaoru Toki, commonly called Toki-san, is a first-year student at Ousai Academy. She becomes Kotomi Tsuda's first friend at the school and is frequently seen with her. Toki projects a gruff, stoic exterior marked by a surly attitude, minimal speech, and a deep, boyish voice, creating an intimidating, delinquent-like impression. This appearance is reinforced by her consistently sloppy school uniform—unbuttoned jacket, untucked shirt, loose tie—and a preference for dark t-shirts, jeans, or baggy shorts outside class. Her long, dark hair is usually in a ponytail with bangs covering her right eye, and she stands notably tall, slightly shorter than Takatoshi Tsuda and initially the tallest female character. Despite this exterior, Toki is inherently polite and kind, demonstrated through actions like properly disposing of litter after a miss or offering her seat to an elderly passenger.

Her perceived delinquency stems partly from embarrassment over chronic clumsiness and a severely poor sense of direction, defining her as a "dojikko". She frequently wears clothing inside out, including her school jacket and judogi, and gets lost easily—searching for the cafeteria, during judo club jogs, or traveling to the Tsuda residence. This clumsiness originates from childhood incidents like accidentally tucking her shirt into her underwear, leading to her preference for loose, sloppy attire. Toki possesses martial arts proficiency, trained in karate, and confidently claims she could defeat five opponents simultaneously. This skill attracts Mutsumi Mitsuba, the judo club head, who recruits her after a match where Toki initially dominates but ultimately loses. The experience reignites Toki's competitive spirit; she joins the club and is later trusted to manage it in Mutsumi's absence. Toki is also academically diligent, putting in extra study effort when needed, and skilled at drawing.

In relationships, Toki and Kotomi share a close bond despite contrasting personalities—Toki introverted, Kotomi lively and perverse. Kotomi often teases Toki about her clumsiness, though Toki readily calls out Kotomi's inappropriate behavior. Toki respects Takatoshi Tsuda, viewing him as intelligent and reliable, and addresses him as "Aniki". She interacts with him normally, and he remains unfazed by her klutzy mishaps. Within the judo club, Toki earns Mutsumi's respect for her skill and determination, though she argues with seniors like Chiri Nakazato over training methods. Toki avoids using names or titles for others, except referring to Takatoshi as "omae no aniki" when speaking to Kotomi and using "senpai" for judo club seniors. Her personal dislikes include sweet foods, and her gender-neutral name "Kaoru" reflects her boyish demeanor.