Shadow Metal

Shadow Metal is a rumored metal which doesn't exist naturally in the world.

Principles
According to Saten Ruiko, rumor has it that when hundreds of esper abilities clash (like during the Daihaseisai), a metal is created which doesn't naturally exist.

Shadow Metal has been shown being generated in several cases from the effects of esper abilities and their interactions with other powers. Two cases occurred during the latter stages of the Level 6 Shift attempt on Misaka Mikoto, against a sphere produced by Misaka Mikoto's out-of-control power, boosted and driven berserk by Kihara Gensei using Exterior and the Misaka Network. When Sogiita Gunha used his power to force open a path for Kamijou Touma, fragments started to form. After the out-of-control power was devoured by the dragons unleashed when Touma's Imagine Breaker was severed, a coating of Shadow Metal was left behind on the ground below.

The Relics, associated with a previous Level 5, have displayed the power to generate Shadow Metal, particles of which also acted as a medium for the esper's ability to control phenomena within the territory they created by enveloping a space. Synthesize Grid, a power associated with one of them, generates the substance as it consumes esper power being exerted within its area of effect. When it was used during a battle at Tokiwadai, the air in the building room covered by the area of effect was flooded with nanometal particles, which acted as a medium for the Relic esper's thoughts and power as well as a means for it to induce phenomena (such as disintegrating targets, stealing heat and moving objects the metal is bound to), the minute metallic dust possessing a high conductivity and with a high level of resultant static electricity.

Daihasei Festival Arc
During the Daihaseisai, Saten Ruiko, having learnt about the rumor concerning Shadow Metal, tried to investigate it, getting into trouble in the process. At that time, the rumor was described as having developed from the increased security to prevent people from stealing DNA maps during the games, apparently baseless.

However, during the Level 6 Shift attempt on Misaka Mikoto and the efforts of Kamijou Touma and Sogiita Gunha to save her, fragments of a metallic substance was formed from the clash between Mikoto and Sogiita's powers when he made a path for Touma to get to Mikoto. After the experiment was stopped, after the dragons unleashed when Touma's arm was severed devoured Mikoto's out-of-control power, Sogiita noticed that the area at ground zero was now covered with a strange metal coating. Aleister Crowley would later retrieve the Shadow Metal, since he watched the fight through UNDER LINE.

Tokiwadai Election Arc
Following the events of the Daihaseisai in September and by the time of Tokiwadai's student council election in October, there had been an increased movement by a group connected to Academy City's previous generation, who used two squares (actually cubes) as their symbol, and apparently sought Shadow Metal, said to exist in the form of cubic crystals.

During the events surrounding the election, Kouzaku Mitori infiltrated a facility which turned out to house one of two cubes referred to as the Relic, which spoke to her and introduced itself to her as the previous #1 Level 5. . Sometime afterwards, an influenced Kouzaku was heading for Tokiwadai with the cube in her hand, and a number of security robots encased in a mound of what appeared to be Shadow Metal behind her.

When Kokuchou Mayui's Relic manifested Synthesize Grid in response to Misaka Mikoto's approach, it started to produce Shadow Metal, a result of the grid consuming esper power. Besides flooding the building with nanometal particles and using them as the medium for remote attacks, it also directly consumed the power exerted by Mikoto close to Kokuchou, as she tried to use electrical precipitation to get rid of the particles in the air, to produce larger chunks of Shadow Metal. After intervention from Kouzaku's Relic and following a clash between the two Relics, Mikoto managed to break through the absorption with a Railgun saturation attack.