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Kirito receiving the World Seed

The «World Seed» (世界の種子, Sekai no Shushi?), is an item that holds a program package called «The Seed» (ザ・シード, Za Shīdo?). The Seed is a free, preset series of program packages that can be used for creating Virtual Reality (VR) worlds as well as control the input and output of the five senses of the players, allowing players to FullDive into the created world. The Seed was created by Kayaba Akihiko and replaced usual proprietary game systems, like the Cardinal System that Akihiko had developed while working for Argus and which was required to run VR games, but had a terrifyingly huge license fee.


The World Seed was given to Kirito by a computerized memory of Kayaba Akihiko, who wanted The Seed to sprout and grow, after Kirito had saved Asuna from the clutches of Oberon. Although Akihiko allowed Kirito to choose what to do with it, after confirming that The Seed was safe to use, he decided to publish it (with Andrew's help) on a server so anyone could download it for free. Using The Seed as a base, cyber technicians around the world could further develop VR worlds.


«The Seed» includes the basic programs needed to create a VR world, such as the audio and video system, as well as a downsized version of the Cardinal System, which was used in Sword Art Online to help in the development and to maintain control of the game. It is made so that the created VR world does not require one large server like the original SAO, but can run on multiple smaller servers.

All games using The Seed as their game engine allow conversion of one account in a Seed-based VR world to another. For example, this ability was used by Kirito when he converted his account from ALfheim Online to Gun Gale Online and back. It allows a player to transfer their data to another game and keep their stats instead of having to start from scratch, but all items and money from the previous game will be lost unless they are given to another player or put in an item storage for safekeeping before the transfer. The whole interconnected network of VR worlds is known as The Seed Nexus.[1]


  • Although Underworld was created using the public version of The Seed, which does not include Sword Skills, they were somehow implemented in the system.


  1. Volume 6 Chapter 11 and Volume 7 Chapter 12