The rare and inexplicable Puberty Syndrome is thought of as a myth. It is a rare disease which only affects teenagers, and its symptoms are so supernatural that hardly anyone recognizes it as a legitimate occurrence. However, high school student Sakuta Azusagawa knows from personal experience that it is very much real, and happens to be quite prevalent in his school. Mai Sakurajima is a third-year high school student who gained fame in her youth as a child actress, but recently halted her promising career for reasons unknown to the public. With an air of unapproachability, she is well known throughout the school, but none dare interact with her—that is until Sakuta sees her wandering the library in a bunny girl costume. Despite the getup, no one seems to notice her, and after confronting her, he realizes that she is another victim of Puberty Syndrome. As Sakuta tries to help Mai through her predicament, his actions bring him into contact with more girls afflicted with the elusive disease. Puberty Syndrome—a rumored, mysterious syndrome that only affects those in their puberty. For example, a bunny girl suddenly appeared in front of Sakuta Azusagawa. The bunny girl's real identity is Mai Sakurajima, a teenage celebrity who is currently an inactive high school senior. For some reason, her charming figure does not reflect in the eyes of others. In the course of revealing the mystery behind this phenomenon, Sakuta begins to explore his feelings towards Mai. Set in a city where the skies and seas shine, Sakuta unfolds the meaning behind his bizarre encounters on women with the said syndrome.