Following the closure of Uranohoshi Girls' High School, the third-year students—Dia Kurosawa, Kanan Matsuura, and Mari Ohara—have just graduated, leaving Aqours with solely the first and second-years. While searching for a new place the remaining members can use to practice, they decide to visit the new school they will soon enroll in. However, to their surprise, the building seems to be abandoned! It turns out that due to the school board's worries regarding how the freshly transferred Uranohoshi students may burden the clubs, they were instead sent to a branch school. This sets Aqours on a new goal—to prove that Uranohoshi students are serious in their clubs as well. Meanwhile, another problem arises: the third-years have unexpectedly gone missing during their graduation trip! Love Live! Sunshine!! The School Idol Movie: Over the Rainbow revolves around the remaining Aqours members as they venture out to search for their missing seniors and, at the same time, try to figure out a way to change the new school's mind.

Everyone has a dream they strive to achieve, and so does the musically talented Kanon Shibuya. However, due to her stage fright, Kanon fails to make it into Yuigaoka Girls' High School's music program and instead ends up in the general curriculum. Even though Kanon makes the conscious decision to quit music altogether, her classmate Tang Keke rekindles Kanon's passion for music with her own: a passion for school idols. Although Keke and Kanon try to form a school idol group, their effort meets strong objections from Ren Hazuki, the daughter of the school's director. Even so, the girls soon visit the director, who allows them to set up their school idol club under one condition—they must win first place at the Yoyogi School Idol Festival. The resilience of these aspiring idols is put to the test as they face the challenges that come their way. Throughout their journey, the girls make new friends and meet new members that join them to become the dazzling idols others can only imagine.

Having decided to walk down a path separate from their inspirations as idols, the girls of Aqours are more determined than ever to shine brilliantly as school idols. With their previous performance marginally increasing the number of prospective students for their endangered school, they look to carry the momentum of their small step forward into the school's upcoming open house and the next Love Live competition. Hoping to use these events to bring more attention to their school, the nine girls look to give their best performances yet. Unfortunately, these small steps forward are not enough to convince Mari Ohara's father from changing his plans. Undeterred by Mari's pleas for reconsideration, the decision to close down the school is made official, putting an end to Uranohoshi Girls' High School's student recruitment, including the open house. Though all hope seems to be lost, the school idols refuse to give up. Faced with impossible odds, Aqours sings, dances, and shines in the hopes of bringing about a miracle.

Manzai is a traditional form of Japanese stand-up comedy where two comedians act out skits as a straight man and funny man, guiding the audience through a series of punchlines. Two determined girls, Mafuyu Kogarashi and Fubuki Kitakaze, are aspiring manzai entertainers who struggle to achieve any real success, despite their lengthy time on stage. They often partner up with manzai newcomers and their close friends—Rin Araya and Nayuta Asougi—to help in the opening acts of each other's routines. In order to eventually reach their desired fame, the four girls challenge themselves by changing venues, switching roles, entering competitions, and giving it their best to hone their craft and gain more experience. But before that can happen, these flourishing young artists must first grow into presentable performers to get signed as amateurs and start their dream in earnest.