Misaka Mikoto

Misaka Mikoto (御坂 美琴 Misaka Mikoto?) (born May 2) is one of the main heroines in Toaru Majutsu no Index and the main protagonist of Toaru Kagaku no Railgun. Introduced in the first volume of the light novels, her role in the story was later expanded in the third volume as well as the release of the Toaru Kagaku no Railgun manga, making her the main heroine of the science side and the second main heroine of the series.

She is the third ranked Level 5 esper in Academy City, and has been nicknamed Railgun due to her signature move. Kamijou Touma coined the nickname Biri-Biri (ビリビリ?) (a Japanese onomatopoeia imitating the sound of electricity), while in the English dub she is referred to as "Bug Zapper", and whenever the two meet, he usually calls her that, even after his amnesia.

source: http://toarumajutsunoindex.wikia.com/wiki/Misaka_Mikoto