"Love Live! Sunshine!!" centers on a group of high school girls from the coastal town of Uchiura who form an idol group called Aqours to save their school from closure. The protagonist, Chika Takami, is inspired by the success of the legendary idol group μ's and decides to create her own group to bring attention to her school, Uranohoshi Girls' High. Chika recruits her childhood friend, You Watanabe, and the shy but talented Riko Sakurauchi, who transfers to Uranohoshi from Tokyo. Together, they begin their journey to become school idols.

As the group grows, they face numerous challenges, including recruiting more members, improving their skills, and competing in the Love Live! competition, a national idol contest. The group eventually expands to include six more members: Kanan Matsuura, a former swimmer with a calm demeanor; Dia Kurosawa, the strict student council president; her younger sister Ruby Kurosawa, who idolizes μ's; Hanamaru Kunikida, a bookish girl with a unique way of speaking; Yoshiko Tsushima, who adopts a self-proclaimed "fallen angel" persona; and Mari Ohara, the cheerful and eccentric half-Japanese, half-Italian school director's daughter.

The narrative explores the dynamics between the members as they balance their personal struggles with their shared goal of becoming successful idols. Themes of friendship, perseverance, and self-discovery are central to the story. The group faces setbacks, such as internal conflicts, doubts about their abilities, and the pressure of living up to μ's legacy. However, their determination and bond as a team drive them to overcome these obstacles.

Throughout the series, Aqours participates in various events and competitions, gradually gaining recognition and support. Their journey culminates in their participation in the Love Live! competition, where they aim to prove themselves as worthy successors to μ's. The story emphasizes the importance of teamwork and the impact of their efforts on their school and community, ultimately highlighting the transformative power of pursuing one's dreams.