In the year 2022, next-generation game Sword Art Online (SAO) is the world's first true VRMMORPG. A virtual reality helmet known as "Nerve Gear" has been developed, making Full Dives into a virtual dimension possible.

SAO has generated worldwide buzz, and on its official launch day, one player, Kirito, immerses himself in its virtual world. But Akihiko Kayaba, the developer of SAO, proclaims the following to all players. "This game is inescapable unless all levels are cleared. And in this world, 'Game Over' is equivalent to death in the real world."