Nao Kadena is a former street racer who becomes a nurse and teacher at Tsujikou, also known as Seirin, in the series Shonan Junai-gumi!. She is introduced as an attractive tall woman with long straight dark hair, standing at least 178 centimeters in height, and has a curvaceous athletic build. A prominent tattoo of the Pieta on her back leads some students to suspect she has ties to organized crime. She is frequently seen wearing red earrings and bright red lipstick.

In her past, Kadena was a celebrated illegal street racer known as the Queen of Hakosuka. She won many races until her younger brother, Kazuhito Kadena, suffered a near-fatal crash during a race with her. The accident left him in a coma and in need of an expensive surgery that he could not survive without. Feeling responsible for his condition, Kadena gave up racing and took a job as the school nurse in order to earn the money for his operation. She is mature and well aware of the effect her appearance has on others, and she does not hesitate to use that awareness to achieve her goals. Her primary motivation throughout the story is securing the funds for her brother's medical treatment, which drives many of her actions and decisions.

In the story, Kadena first appears as a neighbor living a few doors away from Eikichi Onizuka and Ryuji Danma in the rundown Chateau de Riverside apartment building. Shortly after, she asks Danma for a ride on his motorcycle to school, where it is revealed she has been hired as the new homeroom teacher and nurse for Class 1-F, teaching all subjects. She quickly makes an impression by announcing that any male student who achieves a perfect score on a kanji test will be rewarded with a sexual favor; the highest score ends up being only 75, earning the top scorer a so-called boob sandwich for his effort. When the female students grow jealous and one of them, Shinomi, slashes open Kadena's clothing with a razor blade to reveal her back tattoo, Kadena responds not with punishment but by inviting former students of hers who have gone on to prestigious universities to tutor the girls. She frames this as an opportunity for the girls to study hard and get into universities with the most attractive men, which succeeds in motivating them. Later, she attempts to set Shinomi up with Onizuka through an elaborate plan involving a bikini, a cell phone, a television, and Shinomi hiding in a box, but the plan fails when the box is accidentally shipped to someone with a similar name.

Kadena's key relationships include her brother Kazuhito, for whom she is willing to sacrifice her own comfort and security. She interacts frequently with Onizuka and Danma, treating them with a mix of teasing authority and genuine concern. She also forms a close bond with fellow teacher Azusa Fuyutsuki, whom she mentors in matters of womanhood and romance, offering advice and trying to help her mature. After saving enough money for the surgery, Kadena is tricked by an American doctor who takes the money and flees when his illegal activities are exposed in the news. This betrayal leads her to consider resigning from the school. However, after accepting a race challenge from Onizuka and seeing her brother decide to earn the money himself, she changes her mind. She also convinces the school administrator Hiroshi Uchiyamada to allow her to remain in her position.

Kadena is resourceful and pragmatic, willing to sell items at a discount to students and teachers to raise money. She is also adept at reading people and using unconventional methods to encourage and inspire those around her. Her most notable ability is her exceptional skill as a street racer, a talent she largely abandoned after her brother's accident but which she briefly revisits when racing Onizuka. Later in the series, she is seen alongside other faculty members, including the director Ryoko Sakurai, opposing a group from the Ministry of Education involved in a conspiracy.