Mature grade school student Arisu Tachibana is an aspiring idol who receives an invitation from her company president to participate in the Third Entertainment Section—a new idol project. Arisu and eight other young girls soon meet their producer before beginning idol-related activities.

To the girls' surprise, their producer appears to be a childlike adult and nothing like what they had imagined. The producer, who is taking on the position for the first time, also had no idea that he would be meeting a group of short, young idols. The awkward situation leaves Arisu disappointed, and she wishes for a producer change.

However, the producer, with his genuine love for idols and his desire to see them shine, will not let this opportunity pass and expresses that he is serious about working with the girls. Thankfully, the young idols accept the producer after seeing his unwavering passion for idols, serving as the start of their journey to the stage of dreams.

The IDOLM@STER Cinderella Girls: U149 was released on Blu-ray in four volumes from July 26, 2023, to October 25, 2023.