"Love Live! Sunshine!!" is set in the coastal town of Uchiura, where Aqours, a school idol group, is formed by students of Uranohoshi Girls' High School. The story begins with Chika Takami, a second-year student inspired by the success of the legendary idol group μ's, deciding to create her own idol group to save her school from closure due to declining enrollment. Chika recruits her childhood friend You Watanabe and the shy but talented Riko Sakurauchi, who recently transferred from Tokyo, to form the core of the group.

As the group grows, they are joined by additional members: the energetic and confident Kanan Matsuura, her childhood friend Dia Kurosawa, and Dia's younger sister Ruby Kurosawa, who is initially hesitant but eventually embraces her passion for idols. The group also includes Hanamaru Kunikida, a bookish girl with a love for literature; Yoshiko Tsushima, who adopts a self-proclaimed "fallen angel" persona; and Mari Ohara, the cheerful and eccentric student council president with a mysterious background. Together, these nine girls form Aqours and embark on their journey to become successful school idols.

The narrative follows Aqours as they face various challenges, including internal conflicts, self-doubt, and the pressure of competing in the Love Live! competition, a prestigious idol tournament. The group must balance their personal struggles with their commitment to each other and their shared goal of bringing attention to their school. Key moments include their first live performance, overcoming setbacks in regional competitions, and ultimately qualifying for the national Love Live! stage.

Throughout the series, the characters' individual growth is highlighted, with each member confronting their fears and insecurities. Chika's determination and leadership drive the group forward, while Riko's musical talent and You's unwavering support provide a strong foundation. Kanan, Dia, and Mari's complex relationships and shared history add depth to the group dynamics, and Ruby, Hanamaru, and Yoshiko's personal journeys reflect their evolving confidence and sense of belonging.

The story also explores themes of friendship, perseverance, and the importance of chasing dreams despite obstacles. Aqours' journey is marked by both triumphs and failures, but their bond as a group remains central to their success. The series concludes with Aqours achieving their goal of performing at the Love Live! finals, leaving a lasting impact on their school and community while inspiring future generations of idols.