Kuroko Shirai is a major character in the A Certain Magical Index franchise, being the deuteragonist of A Certain Scientific Railgun. She is a Level 4 esper and a member of Judgment serving as a part of the 177th Branch Office. Kuroko is also a student at Tokiwadai Middle School and is the roommate and best friend of the level 5 esper Mikoto Misaka.