Koudo Ikusei Senior High School appears to be a utopia on the surface, offering students unparalleled freedom and boasting a high rank in Japan. However, the harsh reality reveals a less-than-ideal situation. The student body is divided into four classes - A through D - each ranked according to merit, with only the top classes enjoying preferential treatment.
Kiyotaka Ayanokouji finds himself in Class D, the category for the school's perceived underachievers. There, he encounters the reserved Suzune Horikita, who believes she landed in Class D by mistake and aspires to climb to Class A, and the seemingly friendly class idol Kikyou Kushida, whose goal is to forge numerous friendships.
While class assignments are permanent, class rankings are not; lower-ranked students have the opportunity to rise by outperforming those in higher classes. Furthermore, Class D operates without restrictions on the methods students can employ to advance. In the competitive environment of this cutthroat school, can they overcome the challenges and ascend to the pinnacle?