Jailbreaker Arc

Jailbreaker Arc (獄門開錠 (ジェイルブレイカー)  編) is a story arc in the Toaru Kagaku no Railgun manga series, covering chapters 98 onward.

The story focuses on a jailbreak trial organized by the operators of a new private juvenile hall in Academy City in order to test the facility's security features. The challenge is to break into the facility and successfully extract the target prisoner, with a one billion yen reward for successful completion. Various people wish to take advantage of the opportunities presented by this event, both openly and secretly.

The New Juvenile Hall
The new juvenile hall was the second such facility set to open in Academy City, but unlike the publicly-run Reformatory, this juvenile hall was run by a private security business. It was built in response to a rise in crimes committed by espers as opposed to those involving Skill Outs and a belief that the private firm could provide a better service than the publicly-run facility.

The outer wall is 15m tall and encloses the facility in the shape of a right trapezoid. There are two entrances; the main gate where suspects are brought in and which staff use to go in and out, and a back gate which is normally kept closed and only opened in emergencies. The main gate is the only one which vehicles can pass through. It is apparently 1.8 times as strong as the previous Reformatory's gate and there are two additional shutters of the same strength which can be closed behind it. Wind machines installed in the wall can be used to blow projectiles off course. There are pipes running through the wall, which carry a fast hardening filler known as Birdlime (バードライム) to rapidly seal up any holes made in the wall. There are also sensors and defenses in the wall ducts. In the grounds between the perimeter fence and the outer wall, aside from robots, there are numerous acoustic weapons and adhesive pitfalls.

The prison and holding centers are both located within the walls, with an internal division between the two, so as to keep prisoners under the effects of the jammers while being transported between them. For some cases, trials are held online with the prisoner remaining in the facility throughout.

The juvenile hall has a large complement of guard robots, which come in several varieties:
 * The standard guard robots have a domed body on a crescent-shaped base with three legs and a translucent front covering sensors and circuitry.  A weapon block is located on the left side of the robot, capable of firing impact rounds, electrified nets and liquid shots.  There is also a variant which is equipped with a rubber bullet gatling gun instead. The robots are also equipped with speakers and bar scanners. They can travel along the side of the wall on their base, with their legs folded up behind them.
 * There are larger, bipedal robots, referred to as war armadillos, which are also capable of moving around rolled into a ball. They are equipped with a heat blade and air gun held in arms behind the head, as well as an acoustic weapon housed in the chest. Meant to keep intruders out, they are stationed at the outer wall.
 * Type: Hunting Wasp (タイプ:ハンティングワスプ) (T:HW): Flying riot suppression robots in the shape of wasps, with a stinger which injects a sleeping drug.
 * Type: Giant Centipede (タイプ:ジャイアントセンチピード) (T:GC): A robot in the shape of a giant centipede, which constricts targets to restrain them.
 * The largest of these security robots, referred to as riot suppression gigapedes, are stationed inside the prison buildings. Being a robot operating in the solitary confinement area and well within the jammer range, it is intended to deal with inmates who are unable to safely use their esper abilities.

There are also quadrupedal guide robots within the walls, designed by Kyougoku, which have his face on them and somewhat resemble a.

The Jailbreak Trial
In order to promote the new juvenile hall and test its security features, Director Kyougoku Ryouta invited interested espers to challenge the facility and search out vulnerabilities in a Jailbreak Trial (脱獄トライアル). The objective of the challenge was to break into the facility, find and retrieve a target prisoner (played by one of the jailers and located in the girl's building),  and then break out of the facility with them. The reward for successfully completing the challenge was one billion yen.

The exact victory conditions have been noted to be somewhat vague, likely because the organizers didn't expect anyone to complete the challenge successfully. However the facility's defenses were to operate at combat specs during the event, and competitors had to sign a liability form, stating that the organizers were not responsible for any injuries or death occurring as a result of their participation. The rules state that competitors don't have to use the main gate and if they are using equipment too large to carry, to pick it up from the neighboring parking lot.

During the trial, the actual prisoners were apparently moved to the bottom two levels of the prison building basement, while the test prisoner was positioned alone on the top level of the basement.

During the interview where he announced the jailbreak trial, Kyougoku boasted that his company had built defenses to hold even a Level 5 and that even if the likes of Tokiwadai Middle School gathered all of their students, he doubted they'd even breach the first wall. This prompted several Tokiwadai students to enter, including Misaka Mikoto.

Competitors
The challenge and its rewards attracted 4,378 people from various backgrounds and using a variety of methods to attempt the trial.

Notable competitors include: