Seventeen-year-old Suzu Naito lives with her father in Kochi Prefecture's rural countryside. Her childhood featured a deep bond with her mother, who fostered her early passion for music and singing. This connection shattered tragically at age six when Suzu watched helplessly as her mother sacrificed herself to save a child during a flood. The trauma left Suzu resenting her mother's choice, triggering severe nausea whenever she attempts to sing. This grief created lasting emotional distance from her father and diminished her social interactions.

Suzu possesses russet brown eyes, pale skin, and dark brown bob-cut hair adorned with scattered freckles across her cheeks. Her standard attire is her school uniform: a white t-shirt, red tie, blue plaid skirt, white quarter socks, and black loafers. Casually, she wears a white t-shirt, blue jeans, grey sneakers with yellow laces, and adds an ecru scarf or grey pullover in colder weather.

Prompted by her best friend Hiroka Betsuyaku, Suzu enters the virtual world "U." Biometric analysis generates her avatar "Bell," featuring rose-pink knee-length hair, blue eyes, and reddish-pink freckles. Initially named for the English translation of "Suzu" (meaning "bell"), users later nickname her "Belle" (French for "beautiful") as her fame surges. Within U, Suzu miraculously regains her singing voice, performing original songs like "Gales of Song" and "Swarms of Song" that deeply resonate with audiences. Hiroka acts as her self-appointed manager and producer.

Suzu's real-world connections include Hiroka, who champions her musical rebirth; Shinobu Hisatake, her childhood protector and longtime crush; popular classmate Ruka Watanabe; and sports-focused peer Shinjiro "Kamishin" Chikami. Suzu later helps facilitate a romance between Ruka and Kamishin after misinterpreting Ruka's affections.

Belle's virtual stardom collides with her encounter of "The Dragon," an avatar hunted by vigilantes. Investigating his identity reveals Kei, a junior high student enduring physical abuse alongside his younger brother Tomo. To earn Kei's trust, Suzu discards her Belle avatar during a global U broadcast, singing publicly as herself. When Kei's location is compromised, she travels alone to Kawasaki to intervene physically, shielding the brothers from their father. This act of bravery mirrors her mother's sacrifice, enabling Suzu to finally reconcile with it.

The experience heals her trauma: she rebuilds her connection with her father, accepts Shinobu's shift from protector to equal friend, and permanently reclaims her passion for singing. The name "Belle" also serves the film's thematic link to "Beauty and the Beast," symbolizing her journey towards understanding inner beauty and compassion.