The antithesis to the "dumb blonde" stereotype, Urumi Kanzaki is a prodigy with an IQ over 200. She is also a heterochromatic, possessing different colored eyes: one brown and one blue. However, she is psychologically disturbed, having her fair share of hate toward teachers. Her genius is displayed repeatedly by such abstract actions as the detonation of time bombs (i.e. firecrackers in disposable boxes) and making a harmless snake look like a cobra using paper cutouts. Her intellect is also shown through actions, such as shouting curse words in French and being able to speak fluent Mandarin. On the trip in Okinawa, Toshito Kikuchi noted that she can speak 5 languages, but ironically, she doesn't understand what her Gundam otaku roommates say.
Her hatred for teachers stems from her time in elementary school. Urumi's teacher, Ms. Fujimori, while initially welcoming and receptive, wasn't able to handle her intellect properly, since she went to a second-rate college, and it was her first year teaching. Urumi's constant requests for the teacher's time, both inside and outside of school, as well as the fact that the lessons she wanted to learn from the teacher included extremely advanced, college-level subjects (such as differential calculus) eventually made the teacher snap. When Urumi interrupted Ms. Fujimori's lecture to correct her in front of the whole class, the teacher then told Urumi's secret to her class. While it isn't stated explicitly, it can be deduced that her intelligence is derived from her biological father, when Urumi tells Eikichi Onizuka that her mother had selected a sperm-donor, based on his intellect and nothing more. It is even suggested that her mother took the sperm from an American scientific genius (this information can be gleaned from a scene where Urumi and her mother visited some friends in the United States, and Urumi was led into a dark storage room by a doctor, who explains to her that her father is actually just a bottle of donated sperm); this also explains Urumi's natural, blond hair. Naturally, this caused a great deal of psychological trauma to Urumi, and quite an understandable hatred of teachers. It is still unclear what happened to Ms. Fujimori, as her last appearances in the storyline was begging Onizuka to help Urumi before something terrible happens to her.
She is later found by Miyabi in a small apartment, and hired to torture Onizuka. Formerly a student at Holy Forest for a while, but stopped attending regularly after some time, she begins almost immediately, as she frames him for lechery and sends him to jail overnight, only to appear in class and on his homeroom roster the morning after. Onizuka's frustration with her vastly increases, when Vice-Principal Uchiyamada strictly advises him that he cannot inflict physical harm on her due, to her educational potential. Urumi is eventually able to turn Onizuka into her slave (more-or-less, her "genie") by threatening to have him arrested, after she fakes her death when he accidentally pushes her off a building.
However, all this changes when she encounters her Ms. Fujimori again, awakening her deepest hatred and causing her to direct her wrath at the student body. Onizuka responds by bringing his biker gang to school and "kidnaps" her from class. He is finally able to get through to her by almost killing the two of them by jumping over - and nearly falling into - a gap at a suspension bridge, despite her attempts to convince him that she is not afraid of anything, including death. Onizuka makes her see past her trauma, however bad, just isn't worth messing up the present with (in the manga, he does this by having his biker friends share their life experiences with her). Inspired, she allies with Onizuka, and helps with his troubles.
Despite her switch in allegiance, Urumi continues her feud with Miyabi, until Miyabi reveals her origins to the student body. Urumi retaliates by setting up a web page, where she promises to post pictures of Miyabi in her bathroom (Urumi had earlier placed a hidden camera), after a countdown timer reaches zero. However, the site reveals only a single photograph of Urumi, Miyabi, and Tomoko Nomura during their younger years. Urumi never had any intention of ruining Miyabi; she just wanted to scare her. Urumi attempts suicide at an indoor skiing arena by freezing to death, but Onizuka rescues her. It is after this incident that Urumi considers Onizuka to be her "favorite".
She grows extremely infatuated with Onizuka, to the point of wanting to elope with Onizuka. Urumi takes a more stereotypical role of a character that prefers the use of violence, in response to jealousy - she is often seen beating Onizuka mercilessly every time he tries to fulfill his pervertednes. Urumi states Onizuka should wait for her hormones to start kicking in, because she's sure that she would have a bouncing body by then. Like Noboru Yoshikawa, her loyalty to Onizuka is extremely strong, to the point that she would consider suicide, if he were to leave, believing that her own life is worthless without him around.