Hime Onizuka, more commonly known by her nickname Himeko, is a core member of the Sket Dan at Kaimei High School. She is a seventeen-year-old girl with blue eyes and shoulder-length blonde hair that flips up at the ends. Her signature accessory is a Pelollipop Candy, which she almost constantly keeps in her mouth, a quirk that began when the lollipop stick was mistaken for a cigarette during her days as a feared delinquent. Himeko wears the standard Kaimei High uniform, a white sailor-style shirt with a red ribbon and a blue skirt, which she personalizes with a black choker, a thick studded bracelet, and the Sket Dan wristband. While she originally wore high heels, she later switches to pink sneakers. Before becoming known as Onihime, her hair was black and styled similarly to that of her friend Bossun.

Himeko was born and raised in Osaka, where she began playing field hockey in primary school and continued through junior high. At the age of fourteen, her family moved to Tokyo due to her father's job. She struggled to adjust to her new environment, initially feeling alienated from her classmates. She found friendship with a girl named Arisa, who helped her open up to others. However, Himeko witnessed Arisa with a group of delinquents and believed her friend was being extorted. When she confronted the group to protect Arisa, she discovered that Arisa had hired the delinquents as bodyguards to avoid being bullied herself. Feeling betrayed and humiliated, Himeko lashed out and violently defeated the entire gang with her field hockey stick. This incident earned her the feared nickname Onihime, meaning Demon Princess, and the story of the fight spread quickly, leading to her isolation and a reputation she sought to escape. Determined to leave her past behind, she applied to Kaimei High School, far from her old neighborhood, hoping to live quietly without drawing attention.

Despite her efforts to remain isolated, Himeko was approached by her class representative, Chiaki, and a classmate named Yusuke, also known as Bossun, who persistently tried to befriend her. When Chiaki was threatened by two men, Himeko intervened to protect her, though she found herself outmatched. Bossun’s timely arrival saved them, and Himeko was able to defeat the attackers, who recognized her as Onihime. Expecting rejection after her identity was revealed, she was instead accepted without hesitation by Chiaki and Bossun. Bossun then asked her to form a campus support group with him, saying he needed her strength. Overwhelmed by this acceptance, Himeko finally allowed herself to cry for the first time in years, marking the beginning of her new life as the vice-chief of the Sket Dan.

Himeko has a naturally aggressive, impulsive, and sometimes cranky personality. She often resorts to violence as her first solution to problems, a tendency born from frustration and her straightforward nature rather than cruelty. Despite this, she has a good sense of humor and tries to maintain a positive outlook like Bossun, even if she does not always succeed. She is deeply loyal and takes her responsibilities with the Sket Dan more seriously than her companions. Himeko has a soft spot for small and cute things, often revealing a nurturing and maternal side beneath her tough exterior. Originating from Osaka, she occasionally uses Kansai dialect expressions.

Himeko’s primary motivation is her loyalty to the Sket Dan and the sense of belonging it provides. She is determined to help others and uses her strength to protect those in need, reflecting the support group's mission. Her bond with Bossun is central; she admires his leadership and feels a profound gratitude for his role in changing her life. Although she frequently scolds and hits him, her actions are a form of affection. The relationship is complicated, with strong hints of romantic feelings that she often denies or chooses not to acknowledge. She shares a trusting and supportive friendship with Switch, the group's secretary, and the two often join forces to tease Bossun. Himeko also acts as a mentor figure to younger characters, seeing aspects of her past self in them.

Throughout the series, Himeko experiences significant personal growth as she reconciles with her past as Onihime. She evolves from a solitary, distrustful individual into a sociable and caring friend who has found a place where she is accepted for who she is. Her weapon proficiency is notable; she wields a field hockey stick with remarkable skill and superhuman strength. She has gone through several named sticks including Valkyrie, Cyclone, and her current weapon, Flagrance, all made by the BLAST company. Beyond combat, she is also a surprisingly good cook, as discovered during the Gachinko Vivage Battle arc.