World Tree

 «Yggdrasil» is the tree that is at the center of ALfheim Online. Kirito climbs up to the top to rescue the captive Asuna from Fairy King Oberon. The Tribe which reaches the legendary city floating above Yggdrasil and has an audience with the fairy king oberon who lives there is able to be reborn into true fairies, the ALF, the hover limit imposed on the system is eliminated and unlimited flight is possible, and along with it they are capabile of becoming rulers of this infinite sky. It's possible to enter this floating citythrough a dome at the root of Yggdrasail. However, guardian knights who boast of overwhelming strength guard the entrance, one year has passed since the opening of ALO, yet this quest has not yet been cleared.