World Seed

The «World Seed» was given to Kirito after he had saved Asuna from the clutches of Oberon. A computerized memory of Kayaba Akihiko desired that Kirito plant the seed and let it sprout.

Background
«World Seed» is a free program that allows the creation of VRMMORPG. It was originally developed by Kayaba Akihiko and was primarily used in the creation of Sword Art Online. Using the World Seed as a base, cyber technicians can further develop the VR world.

The seed allows conversion of one account in one VR world to another. For example, this ability is used by Kirito when he converts his account from SAO to Gun Gale Online.