"Aikatsu on Parade!" is a crossover anime and manga series that brings together characters from various installments of the "Aikatsu!" franchise, including "Aikatsu!", "Aikatsu Stars!", and "Aikatsu Friends!". The narrative centers around a mysterious phenomenon where idols from different dimensions are summoned to a shared world through a magical gate. The protagonist, Yume Nijino from "Aikatsu Stars!", discovers this gate and becomes the catalyst for uniting idols from across the multiverse.

The story begins with Yume encountering a strange gate during a performance. Upon stepping through, she finds herself in a new world where idols from different dimensions coexist. This world is governed by the Aikatsu System, which allows idols to perform and compete using special cards that grant them unique outfits and abilities. Yume meets other iconic characters, such as Ichigo Hoshimiya from the original "Aikatsu!" series and Aine Yuuki from "Aikatsu Friends!", forming bonds and collaborating to solve the mystery of the gate.

The central plot revolves around the idols working together to stabilize the gate and prevent it from collapsing, which would sever the connections between their worlds. Along the way, they participate in various performances, competitions, and challenges, showcasing their unique talents and styles. The series emphasizes teamwork, friendship, and the shared passion for idol culture, as the characters learn from one another and grow both as individuals and as a collective.

Key characters include Yume Nijino, whose determination and curiosity drive the story forward; Ichigo Hoshimiya, a seasoned idol who provides guidance and inspiration; and Aine Yuuki, whose cheerful demeanor and strong bond with her partner Mio Minato add emotional depth to the narrative. Other notable characters from the franchise make appearances, contributing to the rich tapestry of the crossover.

The series balances episodic performances with an overarching plot, blending lighthearted moments with moments of tension as the idols face challenges both on and off the stage. The narrative culminates in a grand event where all the idols come together to perform, symbolizing their unity and the strength of their shared dreams. Through its exploration of interconnected worlds and the power of collaboration, "Aikatsu on Parade!" celebrates the enduring appeal of the "Aikatsu!" franchise while introducing new dynamics and interactions among its beloved characters.