Destruction of Tree Diagram

The Destruction of Tree Diagram is an event that occurs near the end of the Index Arc, in which the supercomputer Tree Diagram along with the Orihime-1 Satellite was destroyed. Even though information on the true fate of Tree Diagram is only known to a select few, its effect is widespread throughout Academy City in both To aru Majutsu no Index and To aru Kagaku no Railgun storylines.

Tree Diagram
The Tree Diagram is the most advanced and powerful supercomputer in the entire world. Installed on the Orihime-1 Satellite, it was primarily used for weather monitoring with extremely accurate results; so much so, as it can actually schedule what weather condition would occur at a specified time in Academy City.

However, being the most powerful supercomputer it is often used for calculations, though only with the appropriate clearance from authorities; as such researchers like Kiyama Harumi cannot simply use it, and was denied several times for its use. As is the power of Tree Diagram that was extensively used in the Level 6 Shift experiment, where it calculated that only Accelerator could achieve Level 6, and that he would need to kill Misaka Mikoto, the Railgun, 128 times or 20,000 of her clones. As such Tree Diagram was extremely valued by Academy City, and was the seat of Academy City's dominance over the world's technology.

Index Arc
A few mintues after midnight, Kamijou Touma is forced to fight Index in John's Pen Mode after activating the church's failsafe, Necklace, when he negated the spell that would kill Index if her memories were not erased. During the battle Index used Dragon's Breath on Touma; it is a spell that resembles a destructive beam of light, and its after-effects were feathers of light that would doom anyone it touches. After initially forced to fend off her attack, Kanzaki Kaori uses her power to make Index go off-balance. This makes the still in-effect beam to fire skywards, destroying Tsukuyomi's roof; it eventually reaches space and destroys Tree Diagram, which coincidentally was right in its path.

The Tree Diagram Information Receival Center located in the 23rd School District, monitoring the satellite, determines that Tree Diagram disappeared from its projected course at exactly 00:22 of July 28th. Academy City later deploys its search team for the Tree Diagram at exactly 01:15 a.m. of the same day. The first part of the remains of the satellite is later salvaged two days later at exactly 12:40.

Aftermath
Its effects were widespread in Academy City, as people have become used to the scheduling of the weather by the computer, they are now forced to be more wary of the weather. However, the destruction of Tree Diagram itself has affected the whole world. Many countries with space programs have increased their launches into space, seeing the potential to show-off their technology and to steal the remaining pieces after its destruction.

It also becomes a pivotal part in Misaka Mikoto's decision to sacrifice herself for her clones, as she discovers that Tree Diagram has already been destroyed, and has not changed the fact that her clones are still being killed by Accelerator for the Level 6 Shift.

The remaining pieces are also central in the 8th novel of Toaru Majutsu no Index, as several factions try to obtain them, and force Mikoto to try to destroy it, believing that the experiment on her clones may continue. Mikoto's involvement also coerces Shirai Kuroko, a member of Judgment, into getting involved with the dark side of Academy City, as she duels with Musujime Awaki, who holds 'Remnant', the essential core to rebuild Tree Diagram.

'Remnant' was eventually destroyed by Accelerator as he fought Musujime after being requested to do so by Last Order.