It is the year 2022, and full virtual reality has been developed.
Kirito is a player of the VRMMORPG "Sword Art Online". Whilst in the midst of having fun, he and the 10,000 other players logged-in at the time suddenly receive an unbelievable announcement from the system administrator:
The only way log-out is by clearing the game.
Further, getting a "game over" within the game will also result in real death.
Kirito is amongst the first to accept this reality. Foregoing the option of forming parties with other players, he challenges this death-game as a solo player.