Exterior

Exterior (外装代脳(エクステリア)) is a large cultivated brain that greatly boosts Shokuhou Misaki's power. Originally, used as a means for other individuals to use Mental Out, it is later taken over by Misaki for her personal use.

Background
After discovering Misaki's Mental Out ability, the researchers in of the Clone Dolly Workshop decided to instead use the Misaki's powers to brainwash greatmen instead of creating them.

They later take a portion of Misaki's cerebral cortex, cultivated it, and enlarged it. They later cut it in half between the two sides and have them put into two glass tubes with liquid in it.

Prior to Exterior's full completion, Misaki's friend Dolly dies, and here, later learns of the true nature of the project, after taking control of the minds of the researchers, which hoped to get rid of her once Exterior is complete She later has the project crushed completely, brainwashed everyone involved with it, and took it over for her own purposes, apparently filling it with her people loyal to her in order to perform maintenance on it.

Principles
The giant brain was originally intended in the Exterior Project as usable by anyone, whether they are other espers or normal people, any registered person with Exterior gains the ability to use Mental Out. Registration for its usage apparently takes several days, and it is unknown what the requirements are.

Under the control of Misaki it gives her a tremendous boost of her powers. After speaking some commands to it, apparently regardless of distance, she can use her Mental Out from several hundred meters range and absolutely controlling a maximum of 10 people (or from about 100 people as long as they are doing simple commands) to a range of several kilometers, allowing her to put thousands of people under her control.

Daihasei Festival Arc

 * Main article:Daihasei Festival Arc (Railgun)

Misaki can apparently issue Exterior commands in order to greatly increase her mind control abilities. In chapter 59 of the Railgun manga when this is first seen, Misaka Mikoto, who was with Misaki at the time, thinks that the powers granted to Misaki by Exterior far surpass the abilities that a level five should be able to use. It seems as if Shokuhou does not like to rely on the use of Exterior. Moreover, during her command, a small panel of eyes overlayed upon a background filled with liquid and tubes are briefly shown, indicating as a visual representation that it is at least human as the eyes displayed the properties of being controlled by Misaki.

It is later used and taken over by Kihara Gensei in order to facilitate the making of Misaka Mikoto into a Level 6.

Agitate Halation Arc

 * Main article:Agitate Halation Arc

At some point during this arc, when Misaki reveals to Touma the extent of her powers, she makes it clear that she does not have the increased abilities that Exterior allows her to use. She does not explicitly mention Exterior at all.