Shirai Kuroko

is a level 4 esper and student of Tokiwadai Middle School, as well as a member of Judgement. She can usually be found accompanying the third-ranked Level 5 esper Misaka Mikoto- her best friend, partner, and roommate. Though a minor character in Toaru Majutsu no Index, she gets a starring role alongside Mikoto in the Toaru Kagaku no Railgun sidestory.

Appearance
Kuroko is a girl with light brown hair tied into two pigtails; the rest of her hair is 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. She is equally blunt and honest when it comes to her sexuality, oblivious (or rather, uncaring) of the discomfort that her aggressive expression of lesbianism causes in others, even Mikoto, the target of her lust.

Her desire can be aroused by anyone who even resembles Mikoto, even her beautiful young mother Misaka Misuzu. It is for this reason that Mikoto tries her best to keep the existence of her "sisters" a permanent secret from Kuroko.

Although usually laid-back and friendly, Kuroko portrays determination when she encounters enemies, even to those whom she knows is more powerful than herself. To her credit, she is an honorable girl who keeps her word, is kind to children, and shares with Mikoto the same ironclad sense of justice that makes neither of them ever back down in the face of adversity.

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 apparently in love with Misaka, whom she calls "Onee-sama" (big sister); she is on 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.

Index and the Church of Necessary Evil
Her first debut was in the 1st arc where she is on patrol investigating some strange incidents happening in the city due to Stiyl and Kaori in the Anime. This is not in the Light Novels.

Sisters
She makes her first appearance to Touma in the 3rd volume where she's shocked to see Mikoto is 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.

Kazakiri Hyouka and the Imaginary Number Sector
Kuroko is seen hunting down Sherry Cromwell, who had entered the city illegally, and tries to apprehend her but is stopped by her golem. She is saved by Mikoto who also happens to be 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 is preparing to fight of Sherry.

Musujime Awaki and the Remnants of Tree Diagram (Light Novel Volume 8)
Kuroko faces off against Awaki Musujime who has a remnant of the Tree-Diagram, but is out-classed as Awaki proves to be the better teleporter. Awaki teleports a corkscrew into Kuroko's side, as well as several spikes, and even shoots her with a gun. Kuroko returns the favor back at Awaki during their second encounter, but due to Kuroko being on the move all night without rest, she finds she cannot teleport anymore and so she resorts to psychological tactics against Awaki. Awaki's accuracy starts to fail, but then she decides to teleport a 4.5 ton object onto Kuroko. Kuroko, unable to do anything, is saved by Touma who uses his Imagine Breaker to stop the teleport. Kuroko is then taken to the hospital.

At the hospital, Touma visits to see how she is healing up, and accidently walks in when Kuroko is changing clothes. He is rewarded with a slap from Mikoto (With electricity accompanying it). Later Kuroko jokes that Touma likes girls who are less aggressive, but after seeing Mikoto take the suggestion seriously, she gets upset thinking Mikoto really has fallen in love with Touma. Kuroko vows silently to herself to get stronger herself so that Mikoto will rely on her more, and not be a burden after the 'Tree Diagram Remnant' incident.

Oriana Thompson and the Daihasei sports festival (Light Novel Volumes 9-10)
Kuroko is unable to participate in the Daihasei festival due to her injuries from the Remnants incident, and is in a wheelchair during the course of events, escorted by Uiharu. She is seen to cheer up for Mikoto who is taking part in a competition between schools. After seeing Mikoto taking care of Touma on a public TV screen, she vows to kill him for taking advantage of Mikoto and stealing her rightful place.

The Way of Light and Darkness
Kuroko is next seen doing office jobs with Kazari Uiharu and wonders about the strange situation in Academy City, although she is shown to be aware of the news of an intruder due to television announcements.

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 and also because during the emission of the episode was during U.S.A. presidential elections.