"UniteUp! -Uni:Birth-" centers around a group of aspiring idols navigating the competitive world of entertainment. The story begins with Aoi Shindo, a reserved high school student with a hidden talent for singing, who is discovered by a talent agency during a local performance. Reluctant at first, Aoi is persuaded to join the agency’s new idol unit, Uni:Birth, alongside two other members: Haruto Kanzaki, a charismatic and confident performer with a strong stage presence, and Ren Amamiya, a skilled dancer with a mysterious past. Together, the trio embarks on a journey to achieve their dreams while overcoming personal challenges and the pressures of the idol industry.

The narrative explores the dynamics within Uni:Birth as they train, perform, and grow both individually and as a group. Aoi struggles with self-doubt and the fear of failure, often clashing with Haruto’s bold and ambitious nature. Ren, meanwhile, harbors secrets about his past that threaten to disrupt the group’s unity. As they participate in competitions, face rival idol groups, and build their fanbase, the members of Uni:Birth must learn to trust one another and confront their insecurities.

The series delves into themes of friendship, perseverance, and the pursuit of dreams, highlighting the sacrifices and challenges inherent in the idol lifestyle. Supporting characters, such as their manager, Yui Tachibana, and rival idol groups, add depth to the story, creating a multifaceted portrayal of the entertainment industry. Through its blend of personal growth, interpersonal drama, and high-energy performances, "UniteUp! -Uni:Birth-" offers a compelling look at the journey of young idols striving to make their mark in a demanding and often unforgiving world.