Kamijou Touma is a first-year high school student in Academy City, officially classified as a Level 0 esper due to his unique ability's undetectable nature. His right hand wields "Imagine Breaker," negating supernatural phenomena—magic, esper powers, divine blessings—upon contact. This negation cancels his own luck, causing extreme misfortune manifesting as constant accidents, financial struggles, and frequent hospitalizations, prompting his frequent exclamation "Such misfortune!" (*Fukou da!*). Imagine Breaker only affects supernatural forces directly; it cannot negate their physical consequences or purely natural threats. Severing his right arm lifts the ability's suppression, releasing either draconic entities or an invisible force that instilled terror in adversaries like Fiamma of the Right. His arm regenerates afterward, restoring Imagine Breaker.

Born outside Academy City, Touma faced childhood ostracization due to a perceived "jinx" aura, even surviving an attempted stabbing. His father enrolled him in Academy City after kindergarten to escape superstition-driven persecution, later revealed as part of director Aleister Crowley's scheme to utilize Imagine Breaker. Within the city, classmates value him for absorbing their collective misfortune yet resent his unintentional appeal to females—dubbed "Kami-yan disease"—whereby girls sympathize with his plight or are drawn to his actions. Despite attracting affections from figures like Index, Misaka Mikoto, and Shokuhou Misaki, he remains romantically oblivious, preferring "elder sister" types, his self-deprecating view contrasting with his reputation.

Touma's defining trait is an instinctive drive to protect others, summarized by his credo: "I don’t need a reason to save someone." He intervenes in crises regardless of personal risk, often sustaining severe injuries. This ethos persists after losing his pre-series memories during Index's rescue, concealing his amnesia to avoid causing distress. He relies on residual emotional instincts and adopts a cautious social demeanor to mask memory gaps. His moral stance transcends conventional "good vs. evil"; he opposes harm to innocents but aids former enemies like Fiamma or Othinus if deeming their circumstances deserving. His actions frequently disrupt larger conspiracies, inadvertently advancing Crowley's plans.

Key relationships include his guardianship of Index, whom he houses despite her chaotic presence; his dynamic with Misaka Mikoto, whom he first encounters defending thugs from her retaliation and later stops from suicide; and his fragmented bond with Shokuhou Misaki, whose memory he lost after shielding her, resulting in anterograde amnesia specific to her. Allies like Stiyl Magnus and Accelerator originated as adversaries he defeated. His combat style leverages pragmatism and precognition-like reflexes to exploit Imagine Breaker’s limits—such as disrupting sustained abilities—rather than formal training. He wears his school uniform unbuttoned with an orange shirt, sometimes mistaken for a delinquent.

Post-amnesia development includes distrust after realizing manipulation in conflicts like Baggage City, though he reaffirms his core ethos when challenged by Leivinia Birdway. During the Omega World arc, he initially accepts Othinus's "perfect" reality but ultimately rejects it to restore his original world, valuing personal agency over imposed peace. His surname "Kamijou" bears alternate readings: "神浄討魔" (Purifier of God and Slayer of Demons), "神上" (Above God), and "透魔" (Invisible Demon)—the latter reflecting the entity within his right arm.