After escaping Sword Art Online, the forbidden VRMMORPG of death, Kirito returns to reality to find that his game partner and lover, Asuna Yuuki, has not returned and his only clue to her virtual whereabouts is a mysterious screenshot than leads him into the new VRMMORPG world of ALfheim Online.

In the year 2022, some six thousand gamers excitedly explore the new Sword Art Online, which manipulates users' brain waves to create a wholly realistic gaming experience, but soon learn it lacks a log-out button and to escape they must conquer all one hundred floors--or die trying.