Kaoru Toki, a first-year student at Ousai Academy, becomes Kotomi Tsuda's first friend. She stands tall with a boyish build, sharp light brown eyes, and dark shoulder-length hair usually tied in a ponytail. Long bangs obscure her right eye. Her uniform remains perpetually disheveled—shirt untucked, jacket unbuttoned, tie loose. In summer, she layers a dark t-shirt beneath her open uniform shirt; off-campus, she favors dark tees with jeans or baggy shorts.

Despite her surly demeanor, deep voice, and delinquent-like appearance, Kaoru is inherently polite and considerate. Small acts reveal her kindness: retrieving litter after a missed trash toss or offering her train seat to an elderly man. Her gruff exterior partly masks embarrassment over chronic clumsiness and extreme directional cluelessness, which trigger mishaps like inside-out jackets, getting lost on judo club jogs, or boarding wrong trains. A childhood incident involving her shirt tucked into underwear fuels her loose-clothing preference.

Trained in karate, Kaoru boasts she can take down five opponents at once. This skill catches judo club head Mutsumi Mitsuba's attention. After a spar where Kaoru dominates initially but loses, Mutsumi recruits her. Though initially indifferent, the match rekindles Kaoru's competitive drive, leading her to join the club. She eventually earns Mutsumi's trust to manage it during absences. Kaoru diligently applies herself in both athletics and academics, putting extra effort into studies when needed.

Her closest bond is with lively Kotomi Tsuda, whose extroversion contrasts Kaoru's reserve. Their dynamic features Kotomi teasing Kaoru's clumsiness while Kaoru bluntly calls out Kotomi's perverse tendencies. Kaoru deeply respects Kotomi's brother Takatoshi, addressing him as "Aniki" and valuing his reliability; Takatoshi remains unperturbed by her frequent blunders. Within the judo club, she respectfully challenges seniors like Chiri Nakazato on training methods but maintains professional boundaries.

Additional traits include disliking sweets, skill in drawing, and avoiding names unless referencing Takatoshi to Kotomi or using "senpai" for upperclassmen. Her attempts to appear cool often misfire—dramatically donning an inside-out jacket or botching a coin flip. Her gender-neutral name "Kaoru" aligns with her androgynous presentation.