The Cardinal System (カーディナル・システム), or simply Cardinal, is the game engine for almost all VRMMORPG games in the Sword Art Online series. (A game engine manages all the game's resources, processes, and events, and can be simply defined as the works of a game's world.) Kayaba Akihiko designed the original system. He made it more user-friendly for beginners and modders so that it could be more easily distributed in the form of the World Seed that Akihiko eventually gave to Kirito.

Game management

The incredibly deep, multi-threaded Cardinal System was programmed to handle the entirety of Sword Art Online, including real-time item and currency rebalancing, monitoring players' mental states, modifying the world as needed, and generating new quests and even new non-player characters. The only other massively multiplayer online VR game with the same level of complexity was ALfheim Online, but the resource-intensive quest and AI generation routines were disabled until control of the game was transferred to Ymir.

Quest Creation

The full Cardinal system is capable of creating new quests based on stories found online, which of course led to multiple immersion-breaking quests in SAO. It also sometimes required restructuring the game world for everyone, following the completion of some players' most important quests. For example, in the second season of the TV anime, the Excalibur quest resulted in the destruction of the World Tree in Salvation, along with the loss of players' homes and items.

Gameplay Management

Any version of the Cardinal system's self-balancing feature includes ways to resolve balance issues that operate as a separate system process that constantly checks for remaining design problems. A player who found an easy group of enemies with a solid XP boost would have their XP adjusted later; a system glitch would be fixed, or the Administrator would be summoned in non-trivial cases. It would even generate new AI-based characters (such as Freyja and her sisters in the Excalibur quest) that were complex enough to react like a normal person to unexpected input—for example, Sculd, a non-speaking NPC, waved and sent out divine sparks in response to Klein's sudden confession of love. The friendly AI Yui who became the daughter of Kirito and Asuna's characters was also generated by the Cardinal in SAO.

Monitoring

The Cardinal system's monitoring processes run in parallel to detect bugs and track players' mental states.

Emotional tracking

The original NerveGear could analyze the player's brainwaves to gather data on their emotional state. An AI process, Yui-MHCP001, was created by the SAO beta cardinal to mine the data and potentially help troubleshoot any issues that might arise. However, for the official launch, Kayaba Akihiko had changed Yui's permissions so that she could not interact with players and would only monitor and analyze.

Cardinal could also sometimes use an unusual mental pattern to alter the landscape, objects, and other players' avatars for analysis. For example, when Asuna and Kirito solved the murder mystery, they saw the ghost of victim Griselda smile at them from her grave for a few seconds, which is believed to be the effect "echoing" her wedding ring and the landscape.

Alicization

In the Alicization arc, the Cardinal System was used by the Underworld . During the Axiom Church's organizational activity, its administrative control was largely overridden by the church's founder, Quinella, who accidentally projected most of Cardinal into her Fluctlight. As a result, Quinella developed a split personality, causing the entire error monitoring and correction process to appear as a semi-independent side of her consciousness. The error-controlling person decided that Quinella's balancing control was out of balance and needed to be corrected. Later, the person obtained a body of their own.

References

Cardinal System - Fan Wiki