To Aru Majutsu No Index is set in an alternate Earth-like world where two opposing supernatural forces are constantly in a precarious state of balance, ready to set off a clandestine war at any moment. On one side, scientists and academics have created a vast "Academy City" where people's latent psychic powers are coaxed to the surface through education and training. On the other side, both organized religions and cabals of sorcerers alike wield arcane powers manifested through various religious and occult rituals.
Those who awaken their psychic abilities find themselves unable to safely perform magic, while those who devote themselves to magic view espers with jealousy and mistrust. The prevailing opinion is that to coexist, both science and magic must be kept strictly separate, and never mingle. Both societies have individuals who believe that the two sides should work together more directly, and others who believe that the world isn't big enough for both to endure, even carefully separated.