"The IDOLM@STER Cinderella Girls U149" centers on a group of young aspiring idols who are part of the Cinderella Project, a talent development program run by the production company 346 Pro. The series focuses on the "U149" unit, named for its members who are all under 149 centimeters tall. The narrative explores their journey as they navigate the challenges of balancing their dreams of becoming idols with their everyday lives as children.

The protagonist, Arisu Tachibana, is a cheerful and determined 10-year-old who dreams of becoming a top idol. She is joined by a diverse cast of characters, each with unique personalities and backgrounds. These include the shy and reserved Rika Jougasaki, the energetic and mischievous Kanako Mimura, the mature and responsible Chieri Ogata, and the quiet yet passionate Miria Akagi. Together, they form the U149 unit, guided by their producer, who supports them in their growth and development.

The story delves into the personal struggles and aspirations of each member as they work to overcome their insecurities and improve their skills. Themes of friendship, perseverance, and self-discovery are central to the narrative. The series highlights the importance of teamwork and mutual support as the girls face various challenges, from rigorous training sessions to public performances. Their journey is marked by both triumphs and setbacks, reflecting the realities of pursuing a career in the competitive world of idol entertainment.

Throughout the series, the U149 unit participates in various events and activities, including live performances, photo shoots, and promotional campaigns. These experiences allow the characters to grow not only as idols but also as individuals. The narrative emphasizes the balance between their professional ambitions and their personal lives, showcasing how they manage school, family, and friendships alongside their idol activities.

"The IDOLM@STER Cinderella Girls U149" provides a heartfelt and engaging portrayal of the idol industry from the perspective of its youngest participants. The series captures the innocence, determination, and camaraderie of its characters, offering a nuanced exploration of their journey toward achieving their dreams.