"Mob Psycho 100" centers on Shigeo Kageyama, a middle school student nicknamed "Mob" due to his unremarkable appearance and demeanor. Despite his ordinary exterior, Mob possesses immense psychic abilities, which he struggles to control. These powers grow stronger as his emotional state intensifies, particularly when his emotions reach 100%, leading to explosive and often destructive outbursts. To manage his abilities, Mob works as an assistant to Reigen Arataka, a self-proclaimed psychic who runs a dubious exorcism business. Reigen, though lacking genuine psychic powers, serves as a mentor figure, offering Mob guidance on using his abilities responsibly and navigating life.

The narrative explores Mob's journey of self-discovery and personal growth as he grapples with his powers, his desire for a normal life, and his relationships with others. Key characters include Ritsu Kageyama, Mob's younger brother, who initially envies Mob's psychic abilities but later becomes a supportive ally. Other significant figures include Teruki Hanazawa, a fellow psychic who transitions from rival to friend, and Dimple, a malevolent spirit who eventually aids Mob. The series also delves into the lives of Mob's classmates, such as Tome Kurata and the Body Improvement Club, who provide comedic and emotional depth to the story.

The plot is structured around episodic adventures involving supernatural phenomena, often tied to Reigen's business, as well as larger arcs that challenge Mob's understanding of his powers and their impact on the world. Major storylines include Mob's confrontation with the villainous organization Claw, which seeks to exploit psychic abilities for world domination, and his internal struggles with self-worth and emotional repression. Throughout the series, themes of empathy, personal growth, and the balance between power and responsibility are explored, culminating in Mob's realization that his humanity and relationships are more valuable than his psychic abilities. The series balances action, humor, and emotional depth, creating a compelling narrative that resonates with a wide audience.