Fûko Kuzuha is a student at Seito Sannomiya Private School, a 14-year-old girl whose gentle and earnest nature masks a deep well of quiet determination. She has a medium build, big brown eyes often partially hidden by her bushy bangs, and short brown hair that she typically ties back with a pink bow. Her appearance in the standard school uniform is a familiar and unassuming sight to her classmates.

Fûko is defined by her remarkable clumsiness, a trait that makes her prone to accidents and often leaves her flustered or confused. This physical awkwardness, however, is paired with a strong-willed and selfless personality. Despite her shy and mild-mannered exterior, she is always willing to take on extra work or help others, even at the expense of her own time and dignity, which has led to her carrying a significant portion of the class's public duties. She also harbors private insecurities common to adolescence, such as worrying about the size of her chest compared to her peers. Her innocent and open-hearted nature makes her unfamiliar with the complexities of love, a fact that becomes central to her personal journey.

Fûko's background is marked by loss. Her mother passed away from an illness when Fûko was only six years old, and her father works as a traveling businessman, leaving her to reside in the school dormitories. To honor her mother's memory, who taught her always to smile, Fûko often hides her own sad or troubling feelings behind a cheerful expression, not wanting to upset others.

Her role in the story begins as a student struggling with physical education, unable to run even a short distance without falling. She is the first student to meet the new gym teacher, Hibiki Amawa, on a trial day where Hibiki is tasked with getting her to run 50 meters without tripping. Hibiki’s encouragement allows her to succeed, an experience that leaves her with puzzling new emotions about her teacher, whom she, like everyone else, believes to be a woman. As the series progresses, her admiration for Hibiki’s personality deepens into a powerful romantic attraction. This development throws Fûko into considerable personal confusion as she struggles with feelings of shame and anxiety, believing that being attracted to a woman makes her strange or abnormal, especially when her classmates are beginning to show interest in boys.

This central relationship is the most significant in her life. She forms a close bond with Hibiki, who becomes a source of support and inspiration. An additional layer of complexity is added by the one-sided affection of her classmate, Akira Fukae, who is in love with her. When she briefly encounters Hibiki in his undisguised male form, she develops a strong dislike for him, mistakenly believing he is a pervert fixated on women's undergarments; this only deepens her confusion when she later realizes she loves the "female" Hibiki.

Fûko experiences significant growth through these emotional trials. Her initial shyness gives way to courage. During a fire at the school, she refuses to abandon Hibiki and stays by her side until help arrives. Ultimately, she comes to terms with her feelings, realizing that she loves Hibiki regardless of his gender. In the climax of the series, when Hibiki’s true identity is publicly exposed, Fûko courageously speaks up for him, declaring that her feelings remain unchanged and that she will not forget him. She then chases after the train carrying Hibiki away from the city, showing her final, determined act of love. While she has no special supernatural or combat skills, her notable ability lies in her emotional resilience and strength of spirit, allowing her to overcome her confusion and defend what she believes in, even in the face of public scrutiny.