Toaru Majutsu no Index Wiki
Tree Diagram

Orihime-1 satellite up-close.

The Tree Diagram (樹形図の設計者ツリーダイアグラム Jukeizu no Sekkeisha (Tsurī Diaguramu)?, lit. "Designer of the Tree Diagram") was a super-computer which, according to the best renowned scientists in Academy City, was the best in the world. It served as a powerful computation device for many sectors of Academy City, before its sudden destruction due to unforeseen events.


Use and Capabilities[]

Under the pretext of weather prediction,[1] Tree Diagram was loaded into the satellite, Orihime 1 (おりひめ1号 Orihime Ichi-gō?), to monitor many aspects of the city such as weather patterns and security. The true reason it was loaded onto a satellite orbiting space was to protect it from external enemies, such as terrorists, anti-esper extremists, and industrial spies.[1]

The computer was so powerful that rather than forecast weather, it predicted it.[1] Once a month, it predicts the movement of the particles in the atmosphere of the entire globe and calculates one month's worth of weather in one go.[2][1] The Tree Diagram Information Receival Center located in the 23rd School District is the one communicating with Tree Diagram. They send requests to it and also receive information and data from the satellite.

Another use of this computer is to aid researchers with their experiments, such as drug reactions, physiological reactions, electrical reactions, etc. Permission is very difficult to acquire since the Academy City's Board of Directors are the only ones with access to Tree Diagram. One permitted use of Tree Diagram was for the 'Level 6 Shift' Project.

The machine is so powerful that it would take 25 years for any other machine to catch up to its level.[1]


Remnant (残骸レムナント Zangai (Remunanto)?, lit. "Wreckage") refers to the debris left behind by Tree Diagram after it was destroyed by Index on July 28th of the story's first year.[3] Specifically, it is the core of the supercomputer of the Tree Diagram that can be used to repair it.


Toaru Majutsu no Index[]

Index Arc[]

Main article: Index Arc
Toaru Majutsu no Index E06 06m 04s

Tree Diagram being destroyed by Index's Dragon Breath.

During Touma's fight with Index (while being possessed by John's Pen), Index accidentally directs a Dragon Breath's attack to space and destroys the Orihime 1 satellite, destroying Tree Diagram permanently. Meanwhile, Academy City covers up this incident by announcing that Tree Diagram can't be contacted for an indefinite period.

Tree Diagram Remnant Arc[]

Main article: Tree Diagram Remnant Arc

It was revealed that the core of Tree Diagram still remains, and that the satellite might be reparable if it is retrieved. Several countries in the world started launching their shuttles to recover pieces of the satellite, using the ruse of "showing-off" their space programs to the world and proving their reliability to sponsors.[4] However, Academy City was able to recover the most important part of Tree Diagram, the Remnant.

The Level 4 Teleporter,Musujime Awaki, is sent to retrieve it while Misaka Mikoto -- after hearing that the satellite might be repaired -- tried to stop Awaki on her own. During this incident Shirai Kuroko also met Awaki and fought her twice doing her job as a member of Judgment. Awaki successfully escapes, but is cornered and beaten by Accelerator who unexpectedly snuck out of the hospital at Last Order's request. The core is subsequently destroyed during the fight with Accelerator, and Tree Diagram is now considered beyond repair.

Toaru Kagaku no Railgun[]

Level Upper Arc[]

Main article: Level Upper Arc

It is revealed that Kiyama Harumi requested to use Tree Diagram for certain calculations 12 times for her search on curing her Child Error students before giving up and opting to create the Level Upper Network instead for her calculations.[5] It is later revealed to have been inspired by Mikoto's clones' Misaka Network.[6]

Sisters Arc[]

Main article: Sisters Arc

At the end of her rope in trying to stop her clones from being killed in the Level 6 Shift, Mikoto decides that she will manipulate the calculations of Tree Diagram. Her plan is to manipulate it to produce an error in a simulation between Accelerator and Mikoto fighting, determining that the scientists will rely on Tree Diagram to recalculate the data and create a prediction that doesn't involve the Sisters.[2]

Tree Diagram shattered

Shattered Tree Diagram

She goes to the 23rd School District and breaks into the Tree Diagram Information Receival Center. She discovers there that her plans have been ruined, as Tree Diagram has already been destroyed and yet the experiments continue. Mikoto later determines that since the Tree Diagram calculated that Mikoto will be killed on the 185th move against Accelerator, she needs to die on the first move alone to ruin the experiment, knowing that the Tree Diagram is no longer available for recalculations if such a scenario occurs.[3]

Other Appearances[]

Pseudepigrapha Railgun[]

Toaru Anbu no Conference[]

Main article: Toaru Anbu no Conference

In a short omake comic, a bunch of scientists attempting to create the perfect imitation of Mikoto's physical appearance discover that they have yet to learn what underwear Mikoto wears. They first try to use the Tree Diagram for calculating Mikoto's panties, but is denied by Tree Diagram itself, stating that they shouldn't use it for "stupid things".[7]

In a humorous reference, Chapter 33 of the Toaru Kagaku no Railgun manga, during Mikoto's infiltration of the Tree Diagram Information Receival Center, a report is shown, among other things, referring to the request for Tree Diagram to calculate Mikoto's panties. Mikoto however, doesn't notice this.[3]


  • The Orihime 1 and Hikoboshi II satellites may be a reference to the ETS-VII launched by Japan on 1997, where two of the satellite's body is named Hikoboshi and Orihime.
  • Orihime is the Japanese name for Vega, part of the Summer Triangle together with Altair and Deneb. The naming choice for it and the Hikoboshi II (Japanese name for Altair) may be a reference to Tanabata.



v  e
Academy City
Inhabitants Faculty and Staff Students
Factions and Organizations Board of Directors (Board Chairman) • JudgmentAnti-SkillCooperative InstitutionsUseful SpiderSkill-Out
Locations School Districts School District 1 (Administration) • School District 2 (Military & Law Enforcement Training) • School District 3 (Outsider Accommodation) • School District 4 (Food) • School District 5 (Universities and junior colleges) • School District 6 (Recreation) • School District 7 (Middle & High Schools, Student Accommodations, Hospitals) • School District 8 (Faculty Accommodation) • School District 9 (Industrial and fine arts) • School District 10 (Reformatory, Nuclear Research, Cemetery) • School District 11 (Goods transfer) • School District 12 (Theology) • School District 13 (Kindergarten and primary schools) • School District 14 (Overseas Students) • School District 15 (Shopping & Mass Communication) • School District 16 (Commerce) • School District 17 (Industry) • School District 18School District 19School District 20 (Sports and athletics) • School District 21 (Water storage & Observatory) • School District 22 (Underground development) • School District 23 (Aerospace)
Other Notable Locations School District 7: Windowless BuildingHeaven Canceller's HospitalA Certain High SchoolKamijou ResidenceSchool Garden (Tokiwadai Middle School)
Other: Imaginary Number DistrictReformatoryExternal Connection Terminals
Power Curriculum Program Esper (Level 0Level 1Level 2Level 3Level 4Level 5Level 6 (SYSTEM)) • Personal RealityEsper AbilitiesAIMSystem ScanLevel 6 ExperimentsParameter List
Notable Technology Tree DiagramHikoboshi IIBankAirshipCleaning RobotSecurity RobotWind TurbinePowered SuitNanodeviceSupersonic Passenger PlaneHard Science
Events (Timeline) Regular DaihaseisaiIndependence DayIchihanaransaiSummer City Flood Prevention ProgramAnti-Crime Orientation
Other 0930 IncidentInterceptor ShowAvignon Cleanup OperationWorld War IIIDecember Heatwave48 Hours to Restore OrderEvacuation of Academy CityOperation Handcuffs
Other ScienceExperiments and ProjectsChild ErrorMagic-Science TreatyAcademy City Military
See also: Dark Side of Academy City