Kasumi Toyama and the members of Poppin'Party—their high school band—are now second-year students, but with the new school year comes their latest set of challenges: student council duties, cram school, and part-time jobs, among other things. Furthermore, they are now separated into different classes, and as a result, their free time together is shortened. Looking back, their joyful times together seem like nothing more than an unachievable fantasy when their members are too occupied to even gather in Arisa Ichigaya's basement for practice sessions. As the band ponders over the situation, an unfamiliar girl suddenly emerges, unknowingly pulling them into the spotlight once more. In this rising era of girl bands, Afterglow, Pastel*Palettes, Roselia, and Hello, Happy World! begin to make their appearance as well. Each band, comprised of musicians with their unique personalities, illuminates the stage with its performances. As Poppin'Party returns to the music scene and encounters new friends, the sparkling, heart-pounding music starts to play once again!

As the all-girl band Poppin’Party continues to rise in fame, they find a poster for an event at the legendary Nippon Budoukan. Now determined to participate in the "BanG Dream," Kasumi Toyama and the other members of Poppin’Party aim to reach new heights and prove their worth by performing on that renowned stage. Meanwhile, rival band RAISE A SUILEN dreams of changing the world with "the strongest music," but finds itself in dire straits without a guitarist. Though dozens of potential candidates audition for the role, band leader CHU² believes them to be amateurs and unsuitable for the band. However, there may be one guitarist that lives up to CHU²’s high standards. BanG Dream! 3rd Season features multiple all-girl bands, including Poppin’Party, Afterglow, Pastel*Palettes, Roselia, Hello Happy World!, and now RAISE A SUILEN, as they work to astound fans throughout Japan with their spectacular performances. As the BanG Dream competition draws near, the band members are prepared to captivate audiences with their heartfelt music!