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. She is voiced by Satomi Arai.

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. Whenever she and Misaka are together (despite being in public) she will run up to embrace Misaka and indulging herself on Misaka's body, despite knowing she will get shocked as a momento of her actions. Her tendencies to get intimate with Misaka are often expressed to almost ridiculous lengths. One example would be a time where the two are forced to clean a pool and Kuroko tries to trick Misaka into drinking an aphrodisiac-esque drink, in which she ultimately fails and drinks it herself by accident.

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 tried her best to keep the existence of her "sisters" a permanant 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. There is apparently a rumor about Kuroko and Mikoto that goes "There's this horrifying teleporter in Judgment who'll tear apart your body and soul if she catches you...and there's another that rules over even that teleporter's body and soul - the strongest Electromaster," as stated in episode 1 of To Aru Kagaku no Railgun, although Kuroko has no knowledge of this rumor herself.

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.

Level Upper Arc

 * Main article: Level Upper Arc

Kuroko is seen doing her duty as a member of Judgement detaining espers whose powers were enhanched by Level Upper. Due to injuries she sustained from fighting Level Upper users, she couln't partake in rescuing Uiharu from Kiyama Harumi or help Mikoto fight the AIM Burst.

Big Spider Arc

 * Main article: Big Spider Arc

Kuroko aids Mikoto, Konori Mii, and Kurozuma Wataru in fighting and putting an end to the Skill-Out gang, Big Spider.

Poltergeist Arc

 * Main article: Poltergeist Arc

Index Arc

 * Main article: Index Arc

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 Arc

 * Main article: Sisters Arc

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 Arc

 * Main article: Kazakiri Hyouka Arc

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 appears to help the people stuck in the underground part of the city, teleporting civilians out of the area as Anti-Skill is preparing to fight against Sherry.

Tree Diagram Remnant Arc

 * Main article: Tree Diagram Remnant Arc

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.

Daihasei Festival Arc

 * Main article: Daihasei Festival Arc

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.

Academy City Invasion Arc

 * Main article:Academy City Invasion Arc

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 ability is instant teleportation and she is called a Teleporter (空間移動能力者) because of this. Such an ability allows her to teleport herself and anything in her possession a certain distance in the blink of an eye. In volume 8 it is stated that her powers do have limits, being able to transport a total weight of 130.7 kilograms, to a distance of 81.5 meters from herself. It was revealed in episode 5 of the To Aru Kagaku no Railgun anime that before she went to Tokiwadai Middle School, she could teleport objects and other people, but not herself. She was eventually able to teleport herself sometime after enrolling in Tokiwadai. She is able to teleport objects inside designated targets, allowing her to "throw" the darts she carries on her thighs with perfect accuracy. One disadvantage of her power is that she has to concentrate on where she, the object(s), and/or person she holds will 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 render her powers useless, as demonstrated in her fight against Sherry Cromwell. Aside from her powers, Kuroko mainly relies on her Martial Arts abilities, which emphasizes throws and takedowns that compensate for her small size.

Other Appearances
Kuroko appears quickly for a second in Ookami-san and her Seven Companions (also produced by JC Staff Animation Studios), smiling mischievously at the audience, as a potential bride candidate for the boy millionaire Nezumi Chuutaro.

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.
 * Although usually displayed and used as comedy relief, Kuroko displays a strong constitution, as seen when she is constantly shocked by Misaka, surviving after having her neck dislocated by the Dorm Mother, repeatedly pounding her head on solid objects  in fits of rage/terror/stupidity, and moving actively shortly after her joints are pierced by Musujime.
 * There are hints throughout the Toaru Kagaku no Railgun anime which suggest that Kuroko is fairly adept with a camera, and may possess some degree of skill in photography.
 * Kuroko also got a collection of Misaka Mikoto pictures that keep in album that named as "Onee-san's secret" as shown in Toaru Kagaku no Railgun anime episode 2.