After surviving Sword Art Online and returning to the real world, Kazuto Kirigaya discovers that Asuna is among the players who have still not awakened. An image suggesting that she is being held captive in ALfheim Online, a new fairy-themed virtual-reality game, prompts him to assume his identity as Kirito once again. To find her, he must reach the top of the World Tree, a place believed to be inaccessible. With the help of Leafa, an experienced player he meets during his adventure, he travels through a world shaped by rivalries between fairy races. But behind this enchanting setting lies a conspiracy that directly threatens Asuna and the other players who remain trapped.