Kamijou Touma is a student living in Academy City, a highly advanced place in terms of technology. Despite being gauged as a Level 0 esper (no powers), he possesses in his right hand the Imagine Breaker, an ability that negates any power whatsoever. Touma finds a young girl named Index who is trying to run away from Necessarius, a powerful magic organization that she is member of. Blessed with a photographic memory, she holds 103,000 forbidden grimoires within her head. As science and magic cross paths, Touma must face several dangers amid espers and magicians who appear at the exciting scientific town.