Misaka Mikoto ( 御坂 美琴 ) (born May 2) is one of the main heroines in Toaru Majutsu no Index and one of the protagonists of Toaru Kagaku no Railgun. The main character of the science side of the story was introduced in the first light novel volume, and her role in the story was expanded in the third volume, as well as in the Toaru Kagaku no Railgun manga, making her the second main heroine of the series.
Due to her signature move, Railgun, she is the third-ranked Level 5 esper in Academy City. Kamijou Touma coined the nickname Biri-Biri (ビリビリ) (a Japanese onomatopoeia imitating the sound of electricity) and whenever the two meet, he usually calls her that, even after his amnesia.
In the Academy City, it comes with a power system from Level 0 to Level 5 with the highest Level having the more firepower. Misaka Mikoto is ranked 3rd in the Level 5 that only consists of 7 people.
Now you might ask what does she has to do with electricity. Well her esper power is electric which allows her to be a human railgun that shoots off a coin she got from some arcade. Not only that she is also able to manipulate iron sand with her electric power to her liking for instance, sword, giant monster, floating barrier, and etc. This comes without saying but she is also able to use her electric power to zap humans or even manipulate electronic devices.