In Ganso! Bandori-chan, the world of girl bands has been turned upside down by a bizarre and energetic entity known as BanG Dream Chan, and now this chaotic force calls for a massive reunion. The series brings together the chibi-style characters from all ten main bands of the BanG Dream! franchise in a fast-paced, avant-garde comedy filled with pop-infused cuteness. The story unfolds in short, bite-sized segments, each presenting a surreal, laugh-out-loud scenario where the usual rules of band dynamics no longer apply.

The setting is a vibrant, exaggerated version of the familiar BanG Dream! universe, where members from different groups interact in unexpected ways. The cast is a massive ensemble of fan-favorite vocalists and musicians, including the free-spirited Kasumi Toyama from Poppin'Party, the passionate Ran Mitake from Afterglow, the natural-born idol Aya Maruyama from Pastel Palettes, the noble Yukina Minato from Roselia, the super-rich entertainer Kokoro Tsurumaki from Hello, Happy World!, and many others from Morfonica, Raise A Suilen, MyGO, and Ave Mujica.

Narrative arcs are structured as a series of episodic gags rather than a continuous plot. One early episode follows the disastrous attempt by Kasumi and Arisa to buy a bright red sports car, complete with an argument over optional power mirrors. Another arc focuses on the band Hello, Happy World! holding a regular meeting where they discuss making their activities more globally aligned while their DJ, Michelle, looks on. A different segment sees the members of Pastel Palettes engaging in a game of sugoroku (a Japanese board game) in Kyoto, leading to unpredictable chaos. The series also dedicates segments to more conceptual storytelling, such as an episode titled "Emergence ~growth~," which poetically describes the birth of a song from the silence of the night. Each one-minute episode serves as a self-contained explosion of the unique personalities and running jokes that fans of the franchise adore, celebrating the sheer absurdity of this chibi-filled reunion.