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.
When Mikoto was young, she was tricked into giving the city’s scientist her DNA under the pretense of finding the cure for Duchenne muscular dystrophy when they actually wanted to create military combat clones of her. After discovering that the clones didn’t have the same power levels as Mikoto, they were instead used in a Project called “Level 6 Shift”: fated to be killed by Accelerator in order to create the first Level 6 esper. The events of how Mikoto tried to stop the project are briefly mentioned in the third novel but are later expanded and given more detail in the Toaru Kagaku no Railgun manga. When all of Mikoto’s attempts failed, she contemplates letting herself be killed by Accelerator in order to prove the Tree Diagram’s calculations faulty. However, it is not until Touma intervenes and beats Accelerator, proving him to be really weak. The Level 6 Shift project canceled and the remaining 9969 sisters—the clones—are spared.
After the events of the third novel, she eventually develops strong feelings towards Touma but is unable to express them due to her insecurities and the fact other girls were also interested in him. Even though both she and Touma tend to bicker and argue with each other, they a have sort-of friendly relationship. Both of them have gone on a date (albeit it was result of a bet between the two) and exchange cell phone numbers.
During the events of the 14th novel, she calls Touma who is on a trip to Avignon, in France, when he is attacked by Terra of the Left. Even though his cellphone is damaged, Mikoto is still able to listen and learns a startling revelations from Terra that Touma actually lost his memories and has been pretending to his friends all this time. Confused, she confronts Touma when he returns to Academy City in the 16th novel and forces him to tell the truth. After revealing everything to her including what he has been through, Mikoto is first confused on why does she care about him until she finally realizes that she loves Touma. Realizing she may lose him again, she resolves to help him in any way, including making peace with her rival “The Queen of Tokiwadai,” hoping she will help her try to return his lost memories, and joining him in his battles to keep him safe. Touma, however decides not to get her involved in his burdens since he does not want her to suffer again like she did during the Sisters incident and he also made a promise to Etzali to protect her.