Mikoto Misaka is one of the series' main heroines in Toaru Majutsu no Index series and the protagonist of her side story, Toaru Kagaku no Railgun. A psychic user of Academy City, her powers are ranked Level 5, the highest rank for the most powerful psychic users, and she ranks as third-strongest out of the seven people who hold this rank in Academy City.
She attends Tokiwadai Middle School, a famous girls' school for the rich and elite psychics and one of the five elite schools of Academy City. To most people, she is considered a proper lady, but in reality, she has a short-tempered, prideful, and improper attitude with some tomboyish tendencies and insecurities, a fact few other characters know. She is fond of cute, childish things, such as flowery pajamas and Gekota, the popular frog mascot franchise. She has a strong sense of morals and hates injustice, contrary to what she claims. Her power is to generate electricity; she is powerful enough to cause a blackout in the city, make instant railguns by using coins as projectiles, and use electricity to magnetically attract iron particles around her into a chain-sword whip. She can also manipulate electrical objects such as networks and security systems. She has a one-sided rivalry with Touma, who nicknames her "Biribiri" (ビリビリ, relating to the sound of an electric shock), ever since their first meeting before the events of the first novel when he first dissipated her electricity. Since that incident, she is always trying to have a proper match with Touma and defeat him despite his many attempts to avoid conflict with her.