Cardinal redirects here. You may be looking for the Alicization arc character.
Warning Spoiler Alert: This article or section contains details about plotlines not covered in the anime. Do not proceed unless you wish to be spoiled.

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 MMOs 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. A portable version of the Cardinal System was included in the World Seed to facilitate the easy management of new VR worlds.

Game ManagementEdit

In a few situations, Cardinal is given nearly absolute authority on all matters related to the game that it manages without requiring any human input, whether that be player monitoring, spawn balancing or generation of new quests. The only known game that has the highly advanced Cardinal System that SAO had, is «ALfheim Online» (ALO), but the higher functions of the Cardinal System were disabled, until the game was transferred over to its new management, Ymir.

Quest CreationEdit

Cardinal, or at least the highly advanced version built into SAO and ALO, had the authority to create and manage any number of quests. During the run of SAO, there were reportedly a number of strange and bizarre quests that kept appearing every so often. It was explained that Cardinal oftentimes creates quests based around internet trends, mythology and stories that it acquires from the Internet. The Cardinal running both SAO and ALO 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. This is shown when ALO's Cardinal System creates a quest, in which failure would have led to the destruction of the World Tree, and destroyed player-owned homes and items.

Gameplay ManagementEdit

In addition to creating quests, all versions of the Cardinal System have a balancing system, designed to keep players from exploiting certain aspects of the game. An example would be if a player found an area where monster's respawn rate was low, with high EXP gain, Cardinal would appropriately lower either of the parameters. Cardinal would also check for bugs in the system and attempt to fix them. As an artificial entity, Cardinal is even able to give shape to new AI programs and highly realistic characters such as Freyja and the hyper-intelligent Yui.


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

Emotional MonitoringEdit

Griselda's ghost

Griselda's Emotional Imprint

The AI, «Yui-MHCP001» was created to monitor the mental states of SAO's players, as well as to attempt to remedy them. 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. 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.

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 seen 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.


Human form of Cardinal

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.