Shirai Kuroko

is a student from Academy City and a member of the Public Morals Commitee of the said city. She usually accompanies third-rank Level 5 Misaka Mikoto and she also acts as her backup when she gets into trouble.

Appearance
She is a girl with light brown hair tied into two pigtails; the rest of her hair are left to hang as two rows of fringes divided in the middle. Her pigtails are tied in place by a red bow each.

As per ruling of both Academy City and Judgment, she wears the uniform of Tokiwadai Middle School and the Judgment armband.

On her thighs, she secures a pair of black straps where she stores the metal spikes used to secure criminals.

Personality
Kuroko can be described as a "girl living in the future". She is used to the world 30 years from now portrayed by Academy City and thus, is ignorant to customs that the present-day Japan still practice, like the "umbrella drawing" which students usually use to link their names to the name of their crush.

Aside from being a girl with a modernistic outlook, she can also be blunt when giving her opinions, and this has caused her to be at odds with Uiharu once.

However, Kuroko portrays determination when she encounters enemies, even to those whom she knows is more powerful to her.

Background
Kuroko is Misaka's kouhai in Tokiwadai Middle School. A Level 4 psychic, she is a member of, a special public committee group whose duty is to maintain peace and order in Academy City.

She is in love with Misaka, whom she calls "Onee-sama" (big sister); she is in the constant lookout for a chance to get physically intimate with Misaka (and getting called a pervert in the process), and tends to get jealous if someone else gets her attention; this unfortunately happens to be Touma since he has caught the attention of Misaka for various reasons.

Plot
She's a major character in To aru Kagaku no Railgun, helping Mikoto and friends in dangerous situations. Her first debut was in the 1st volume where she is on patrol investigating some strange incidents happening in the city due to Stiyl and Kaori. She makes her first appearance to Touma in the 3rd volume where she's shock to see Mikoto hanging out with him, giving him a threat to not lay a finger on her. Later, when Touma decides to investigate the Level 6 Shift Project she meets him again at the dorm where she manages to hide him away from one of the dorm supervisors.

in the 6th novel she's hunting down Sherry Cromwell who had entered the city illegally and tries to apprehend her but is stopped by her golem, but is saved by Mikoto who was on the scene. She later helps the people stuck in the underground part of the city, teleporting civilians out of the area as Anti-Skill was ready to fight of Sherry.

During Volume 8 Kuroko faces off against Awaki Musujime who has a remnant of the Tree-Diagram and Kuroko faces off against her but Awaki proves to be the better teleporter. Awaki teleports a corkscrew into Kuroko's side, she teleports her spikes into her as well, and even shoots her with a gun. Kuroko returns the favor back at Awaki during their second encounter, but due to Kuroko running around all night with out rest she cannot teleport anymore so she resorts to psychological tactics against Awaki. Awaki's accuracy starts to fail and then she decides to teleport a 4.5 ton object onto Kuroko. Kuroko unable to do a thing gets saved by Touma who uses his Imagine Breaker to stop the teleport. Kuroko is then taken to the hospital. She is also seen in a wheel-chair during the Daihasei School Festival.

Abilities
Her powers are instant teleportation (and she is called a because of this), which allows her to teleport herself and anything in her possession. In volume 8 it states the limits of her powers to be total weight of the items being teleported not exceeding 130.7 kilograms, and to a limit of distance to a radius of 81.5 meters from her. One disadvantage of her power is that she has to concentrate on where she, the object(s), and/or person she holds would be teleported to, while working out the spacial co-ordinates of jumping between 3-dimensional and 11-dimensional space, so any disturbance in her concentration will make her powers useless, as demonstrated in her fight against Sherry Cromwell.

Trivia

 * In the Index anime adaption (Episode 15) of the Angel Fall arc, Shirai Kuroko is depicted to have switched with the US President Barack Obama, using his phrase "Yes. We. Can". This was not in the Light Novels, and could be seen as a in-joke for the anime producers, considering Kuroko can also mean 'black child' literally in kanji.