The five-part series, which utilizes a 3D animation style, follows a group of superheroes in a world where they must compete for popularity as they achieve worldwide notoriety for unmasking a villain who posed an environmental threat.

"U" is a popular social media platform where people can create a virtual persona and start a new life. Among its five billion users, one newcomer is quickly gaining attention: Belle, a beautiful singer whose alluring melodies slowly capture the hearts of the masses. But in this space where everyone hides behind an avatar, curiosity arises over who the mysterious girl truly is. Suzu Naito—a shy girl from the countryside—can no longer sing following past trauma, all her efforts resulting in breakdowns and illness. However, when Suzu joins U, she is once again able to project her voice. Under the alias "Belle," her vocals soon go viral, receiving both love and hatred. Meanwhile, rumors spread of a chaotic beast within U, known only as "The Dragon." After a chance meeting during her concert, Belle finds he is not as evil as the stories suggest. Now, both online and in the real world, Suzu has to face the struggles of identity, fame, and opening one's heart.

The anime's story will start where the third season left off, at the competition for who will open the Triple S international sporting event. Raging Entertainment's HE★VENS idol group had hijacked the competition between QUARTET NIGHT and ST☆RISH, causing chaos. However, after the QUARTET NIGHT members suggest a certain idea, the three groups aim toward a new stage, with HE★VENS swearing to get their revenge on the other two groups.

Hiyori Suzumi, who left her hometown to continue pursuing her passion of track and field, enrolls in Tokyo's Sakuragaoka High School. In searching for a part-time job, Hiyori ends up becoming an apprentice manager for her classmates Yuujirou Someya and Aizou Shibasaki, who are members of the idol group LIPxLIP. The story follows the struggles that Hiyori faces with school, extracurricular activities, and her managing job, as well as the idol group LIPxLIP as they perform on stage.