"Lesson XX" is a psychological thriller anime that explores themes of identity, morality, and the consequences of unchecked ambition. The narrative centers on a prestigious academy known as the Lyceum, where students are trained in advanced psychological techniques to manipulate human behavior. The academy operates under the guise of fostering future leaders, but its true purpose is to create individuals capable of controlling societal structures through subtle, often unethical means.

The protagonist, Akira Saito, is a brilliant but emotionally detached student who excels in the academy's rigorous curriculum. Akira's cold demeanor and unparalleled skills draw the attention of the academy's enigmatic director, Professor Kuroda, who sees Akira as the perfect candidate for a secretive project called "Lesson XX." This project involves the development of a revolutionary psychological technique capable of rewriting a person's core identity, effectively erasing their past and reshaping them into a new individual.

As Akira delves deeper into the project, ethical boundaries begin to blur. The narrative introduces a diverse cast of characters, including Akira's rival, Haruto Miyamoto, a morally driven student who opposes the academy's methods, and Yuna Takahashi, a former prodigy whose involvement in an earlier iteration of Lesson XX left her mentally scarred. These characters serve as foils to Akira, challenging the protagonist's worldview and forcing confrontations over the morality of their actions.

The plot intensifies as Akira uncovers the darker aspects of the academy's operations, including its ties to a shadowy organization that seeks to use Lesson XX for global manipulation. The story builds toward a climactic confrontation where Akira must decide whether to continue advancing the project or dismantle it entirely, knowing the consequences of either choice could reshape the world. The series concludes with an ambiguous ending, leaving the ultimate fate of the characters and the project open to interpretation.