Blue Flag is a Japanese manga series written and illustrated by Kaito, the creator of Cross Manage. It was serialized digitally on Shōnen Jump+ from February 2017 to April 2020, and publisher Shueisha later collected the chapters in eight tankōbon volumes. A slice-of-life manga set in a high school, Blue Flag tells the story of a group of friends who must navigate personal difficulties, societal expectations, and their feelings for and about each other.