Nayu Hayama is the protagonist of Chu-Bra!! and a first-year student at Ounan Middle School. Her introduction to the school is memorable: during the opening ceremony she trips and accidentally reveals her black lace panties to the entire freshman class. This incident, combined with her open fascination with underwear, leads to rumors and misunderstandings among her peers. Nayu works as an underwear monitor, testing new bra and lingerie products for a company, and she has a deep, instinctive ability to judge whether someone is wearing properly fitting undergarments. She cannot help but point out mistakes when she sees them, a habit that initially alienates others but later becomes the basis for her mission.

Nayu’s passion for underwear is rooted in her personal history. After her parents died, she came to live with her older step-brother Keigo, who works as an underwear designer and often asks her to test his samples. During a childhood period of bedwetting, her grandmother helped her find confidence through well-chosen underwear, which shaped Nayu’s belief that the right underwear is essential for a girl’s comfort and self-esteem. This conviction drives her to want to educate her classmates and help them through the challenging physical and emotional changes of adolescence.

Personality-wise, Nayu is outgoing, confident, and unflinchingly direct. She speaks her mind without hesitation and is not embarrassed by her interests, even when they are considered unusual for a middle-school girl. She is also empathetic and genuinely cares about the well-being of those around her, often putting others’ needs ahead of her own. Her emotional expressiveness is shown through her animated facial expressions and body language.

Nayu’s primary motivation is to spread awareness about the importance of proper underwear. She aims to start an underwear club at school, later forming the Underwear Appreciation Society with the help of her friends and a supportive teacher, Tamaki Mizuno. This club becomes the central activity through which she develops her key relationships. She befriends Yako Jinguuji and Haruka Shiraishi after they initially suspect her of improper behavior. Together they recruit other members, including the fashion-forward Kiyono Amahara. Nayu also works closely with male classmate Hiroki Komachi, who encourages her when her club plans face opposition from a disapproving teacher.

Throughout the story, Nayu shows personal growth in balancing her enthusiasm with social awareness. She learns to communicate her knowledge in ways that others can accept, and she becomes more sensitive to the insecurities of girls like Yako, who is self-conscious about her flat chest, and Haruka, who is embarrassed by her large breasts. Nayu’s role is that of a catalyst: her confidence and specialized knowledge push the other characters to address their own body image issues and to embrace their changing bodies.

Nayu’s notable abilities include a precise, almost professional understanding of lingerie design, fit, and materials, which allows her to give accurate advice. She is also resourceful, using her step-brother’s connections and her own experience to create custom garments when store-bought options do not suit her friends. Though she lacks any supernatural or combat skills, her social boldness and expertise make her the driving force of the group. She remains a warm, determined, and slightly eccentric middle-schooler whose unusual hobby ultimately brings her closer to the people around her.