Tree Diagram Remnant Arc

The Tree Diagram Remnant Arc is a story arc in Toaru Majutsu no Index. Focusing mostly on the point-of-view of Judgment member Shirai Kuroko, it deals with an important piece of the recently destroyed Tree Diagram, the Remnant, being stolen by Musujime Awaki a fellow teleporter, as well as Misaka Mikoto and her clones' struggle to stop the experiment from happening once again.

Tree Diagram

 * Main article: Tree Diagram

After Index unknowingly destroyed Tree Diagram back in the 28th of July, the knowledge of it's destruction was seemingly kept secret by Academy City. However, it became quite apparent with that Academy City could not keep it's demise a secret any longer; such as the inaccurate weather predictions, as well as at some point several countries with space programs, desiring to seek out the remains of the destroyed super computer with under the cover of "showing-off" their space programs to the world, and to prove their reliability to sponsors.

Despite the other countries' efforts, Academy City's space program based in the 23rd School District was successful in recovering the Remnant of Tree Diagram, and hired people from the outside of Academy City to deliver the Remnant, that was encased in a radiation-proof, air-tight luggage bag made out of siliconondrum to the Tokiwadai Middle School Subsidiary Calculus Facility, a code to hide the true recepient of the Remnant. Meanwhile, Awaki Musujime – the guide to the Windowless Building – is assigned by the Science Association to retrieve the Remnant, with this her mission she also receives voluntary aid from her comrades as well.

Other Factors
Meanwhile, both Mikoto and her clones discover that the Remnant has been recovered, and have become worried that the experiment would restart if ever the Tree Diagram would be reassembled as the result of Remnant's recovery. Due to this they started individual efforts in hoping to stop it from occurring again, with Last Order – the administrator of the Misaka Network – giving full support to the clones' attempts to stop it.

Prelude
Kuroko notices Mikoto's unusual behavior, during their shopping of lingerie after seeing the news report regarding the recent influx of countries with space programs launching missions into space, with Academy City launching their rocket last week, though it was later completely disregarded and they returned to do their shopping. Kuroko is later called by fellow Judgment member Uiharu Kazari regarding a recent and unusual robbery, much to Kuroko's dismay since she rather spend time with Mikoto. Before leaving, Mikoto advises Kuroko regarding the weather, saying that it might rain later on, which Kuroko finds both unusual and suspicious.

Trivia

 * With only two episodes, this is the shortest arc the anime adaptation of the novels has featured.