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The Cardinal System operating Aincrad.

The «Cardinal System» (カーディナル・システム, Kādinaru Shisutemu?), occasionally referred to simply as Cardinal, serves as the primary driving and management force of nearly all Virtual Reality Massively Multiplayer Online (VRMMO) games in the Sword Art Online Universe. The system was originally developed by Kayaba Akihiko to manage all resources, processes, and events within Sword Art Online (SAO).[citation needed] A downsized version of the Cardinal System was included in The Seed to facilitate the easy management of new virtual worlds.[1]

Game Management[]

Designed to not require outside maintenance, the Cardinal System autonomously managed the entirety of Sword Art Online, including the operation of non-player characters, the balancing of items and currency, the monitoring of the mental state of players[2], and the generation of new quests[3], via a countless number of lower program bundles under its command.[2] The only known game that has the highly advanced Cardinal System that SAO had is «ALfheim Online» (ALO); however, the higher functions of the Cardinal System were disabled in the latter until the game was transferred over to its new management, Ymir.[3]

Quest Creation[]

The highly advanced version of the Cardinal System managing Sword Art Online and ALfheim Online had the authority to create and manage any number of quests. The quests created by the system are based on legends and stories that it acquires from the Internet, which resulted in a number of strange and bizarre quests continuously appearing every so often in Sword Art Online. The full version of the Cardinal System is also capable of creating quests with the ability to completely change the geography of the game itself, even for those not involved in a quest or event. An example of this is when ALO's Cardinal System created a quest in which failure would have led to the destruction of the World Tree, obliterating player-owned homes and items in the process.[3]

Gameplay Management[]

All versions of the Cardinal System have a balancing system, designed to immediately rectify any issue threatening the balance of the world.[4] If a player found an area where a monster's respawn rate was low, with high EXP gain, Cardinal would appropriately lower either of the parameters.[citation needed] Cardinal would also check for bugs in the system and attempt to fix them.[citation needed] As an artificial entity, Cardinal is even able to give shape to new artificial intelligence (AI) programs and highly realistic characters such as Freyja[5] and the hyper-intelligent Yui.[2]


The Cardinal System had a number of monitoring systems, designed to either detect bugs,[citation needed] or to keep track of the mental health of the players.[2] Cardinal even has a sub-program that continuously checks the main process for errors and corrects them.[4]

Emotional Monitoring[]

Griselda's Emotional Imprint.

An artificial intelligence named «Yui-MHCP001» was created to monitor the mental states of Sword Art Online's players, as well as to attempt to remedy them.[2] The original NerveGear had the ability to read the wavelengths of the brain, and to parse the data, in order to determine what sort of emotions and thoughts were felt.[6] This allowed Yui to determine the emotional state of any player within the game. However, at the game's official release, the Cardinal System denied Yui permission to interact with the players due to orders from Kayaba Akihiko, thus forcing her to continue monitoring the emotions of players without being able to take any action to remedy them.[2]

Additionally, when Cardinal detected an unusual or special brain pattern, it had the ability to imprint that data on the surrounding landscape, items, or even other players' avatars in raw format for analyzing. This essentially meant that a partial duplicate of one's state of mind was saved within SAO. An example of this is when Asuna and Kirito seem to witness the ghost of Griselda smiling at them. This was likely the imprint of Griselda's emotions, left on her wedding ring, and the landscape.[6]


The human avatar of the Cardinal System's sub-process that appears in Underworld.

Main article: Cardinal (Underworld)

In the Alicization Arc, a version of the «Cardinal System» was revealed to have been employed in the creation of «Underworld». However, during the rise of the organization known as the Axiom Church, most of the administrative capabilities of the System were stolen by the Church's founder, Quinella, who accidentally burned the primary instruction of the Cardinal System into her Fluctlight. However, Quinella later developed a split personality from the sub-process of the Cardinal System that was in charge of correcting the errors of the main process and deemed that Quinella was committing a grave error with her methods of maintaining balance. This split personality eventually obtained a body of her own, but was forced to retreat to the Great Library Room that is within the Central Cathedral, but not spatially linked to it.