Kaoru Toki, called Toki-san, enters Ousai Academy as a first-year student and becomes Kotomi Tsuda's inaugural friend there, often appearing at her side. She stands nearly as tall as Takatoshi Tsuda, possessing a boyish physique accentuated by sharp, light brown eyes. Her dark hair falls to her shoulders, typically pulled into a ponytail with long bangs obscuring her right eye. Toki consistently wears her school uniform sloppily: shirt untucked, jacket unbuttoned, and tie loose. In summer, she layers a dark t-shirt beneath her open uniform shirt. Off-campus, she favors dark t-shirts paired with jeans or baggy shorts.

Despite a surly attitude, deep voice, and piercing gaze creating an intimidating first impression, Toki reveals herself as genuinely polite and kind. This contrast emerges when she properly disposes of litter after missing the trash can or offers her seat to an elderly passenger on a train. She embodies the "dojikko" archetype through extreme clumsiness and a notoriously terrible sense of direction. Toki frequently gets lost even in familiar places like school grounds or during judo club jogs, and often wears clothes inside out, including her judo gi. These traits originate from childhood embarrassments, like tucking her shirt into her underwear—an incident she describes as lasting trauma. Her attempts to project coolness often misfire, resulting in mishaps such as punching a coin mid-flip instead of catching it.

Skilled in karate, Toki confidently asserts she can defeat multiple opponents. This ability leads Mutsumi Mitsuba to recruit her into the judo club following a match where Toki initially dominates but ultimately loses. Though initially apathetic, the challenge re-energizes Toki, compelling her to stay in the club. She demonstrates academic determination, studying intensively when required. Despite her klutziness, Mutsumi trusts her to oversee the club during absences.

Toki's closest bond is with Kotomi Tsuda; despite Toki's introversion contrasting with Kotomi's extroversion, they are best friends. Toki frequently serves as the straight man ("tsukkomi") to Kotomi's antics. She respects Takatoshi Tsuda, addressing him as "Aniki" (older brother), and stands among the few girls able to converse normally with him. Within the judo club, she respects seniors like Mutsumi and Chiri Nakazato yet openly debates training methods with them. Her interactions are marked by a reluctance to use names or titles, reserving "senpai" solely for judo seniors.

Further details include her dislike of sweet foods, a talent for drawing, and use of the gender-neutral name "Kaoru." Her surname "Toki" translates to "Time, hour, moment."