Exterior

Exterior (「エクステリア」, Extelia/Exteria/Exterior) is apparently some device that greatly boosts   Shokuhou Misaki 's power 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, Mikoto Misaka, 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 Misaki does not like to rely on the use of Exterior.

Agitate Halation Project Arc (New Testament Volume 7)
At some point during this arc, when Shokuhou 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. Therefore, in all probability, Exterior has been destroyed sometime before this point, probably during the Daihasei arc.