In his final year of high school, Taichi Ichinose finds himself sharing a class with his popular childhood friend Touma Mita for the third year in a row. Meanwhile, Taichi is hesitant to interact with his shy and clumsy classmate, Futaba Kuze, despite seeing her as a reflection of himself.

However, after an encounter in the library brings them together, Taichi discovers that Futaba has feelings for Touma. Initially harboring doubts at the prospect, he decides to help her after she declares an emotional yet firm decision to change. As spring comes into full bloom, the three classmates find themselves in a relationship entangled by intricate emotions and personal conflicts while they navigate through an uncertain future.

Ao no Flag was published digitally as an English simulpub as Blue Flag through MANGA Plus. The series was published physically in English by VIZ Media under the VIZ Signature imprint from April 21, 2020 to June 15, 2021; in Spanish by Editorial Ivrea; in French by Kurokawa; in German by Carlsen Verlag; and in Italian by Panini Comics.

At the 2017 Tsugi no Kuru Manga Awards, Ao no Flag was awarded third place in the web manga division. The manga was nominated as a finalist in the graphic novel category of the 41st Los Angeles Times Book Prizes show. It was also placed in the Top Ten titles of the Young Adult Library Services Association's 2021 Great Graphic Novels for Teens list.