Suzu Naito is a third-year high school student living in the rural
Kōchi Prefecture of Japan, with a lost passion for singing and songwriting. As a child, Suzu witnessed her mother rescue a girl from a flooding river at the cost of her own life and thus resents her for "abandoning" her for a stranger's child. Suzu remains in contact with a group of older choir teachers who were her mother's friends but is alienated from most of her classmates, except her childhood crush and self-appointed protector Shinobu Hisatake, popular girl Ruka Watanabe, sportsman Shinjiro "Kamishin" Chikami, and her genius best friend Hiroka "Hiro" Betsuyaku. At Hiro's insistence, Suzu signs into the popular virtual world "U" and is appointed a beautiful avatar with freckles (through the AI engine's biometric analysis), whom she names "Bell", the English translation of her own name. Upon logging in, she finds herself capable of singing again. With the assistance of Hiro, who appoints herself Bell's manager and producer, Bell becomes a hit on U's music charts, and people start referring to her as "Belle", meaning "beautiful" in French. During one of Belle's concerts, an infamously strong and near-unbeatable user, "The Dragon" (or "The Beast"), arrives, fleeing from the Justices, a vigilante group led by the self-righteous Justin, who fight the Dragon and accuse him of disturbing the peace of U. Justin plans to unveil the Dragon's identity to the public using a specialized program mostly reserved for U's owners. Intrigued by the Dragon, Suzu begins to gather information about him. She discovers that he is popular amongst children, who consider him to be their hero. She meets the Dragon and his five guardians
AIs. Belle and the Dragon grow close. In the real world, Ruka confides to Suzu that she has a crush on Kamishin. Suzu helps the two confess their feelings. In U, Justin captures and interrogates Belle, threatening to unveil her identity to the world if she refuses to cooperate. The Dragon's AIs rescue Belle, but their intervention allows Justin and his group to locate the Dragon's castle and burn it down. The Dragon flees before Belle can find him. Suzu and Hiro work to find out the Dragon's real identity before Justin can and warn him. They find out the Dragon is a third-year junior high school student named Kei who is being physically and verbally abused by his father; Kei's protectiveness over his younger brother, Tomo is what gives the Dragon his unbeatable strength in U. Suzu contacts Kei offering help, but Kei does not believe that she is Belle, and generally distrusts everyone who offers him help, since nobody has ever followed through. Shinobu, Ruka, Kamishin, and the choir teachers reveal their knowledge of Belle's true identity and urge Suzu to sing to gain Kei's trust. Suzu unveils herself to the world in the U and sings. Tomo convinces Kei to trust her and they try to contact her again. When Kei's father sees that evidence of his abuse has been posted online, he terminates their internet connection before Kei can tell Suzu their address. Using context clues, Ruka and Kamishin deduce that Kei's hometown is
Kawasaki,
Kanagawa, near
Tokyo. Since authorities cannot intervene on abuse charges until 48 hours have passed, Suzu locates Kei and Tomo on her own and protects them from their father. The next day, she and her father warmly greet each other at the station. Shinobu praises Suzu for her bravery and deciding she no longer needs his protection, finally feels free to pursue the relationship he has always wanted with her. Finally understanding her mother's selfless actions, Suzu makes peace with her death. ==Voice cast==