One day at the end of the year, Kirigaya Suguha showed her cousin, Kirigaya Kazuto, a news article about the legendary item, the andlaquo;Holy Sword Excaliberandraquo;, being discovered in ALfheim Online. Without delay, he called Asuna, Klein, Lisbeth, Silica and Sinon to challenge the dungeon in the sky of Jandouml;tunheimr, where Excaliber was . After preparing their items at Lisbeth's arms shop and purchasing potions for the adventure, the group entered Jandouml;tunheimr via a secret passageway in Alne. At the end of the tunnel, they reached the top of Jandouml;tunheimr and Leafa called Tonkii, a flying evil-god-class monster that they had befriended several months ago. The group climbed on Tonkii's back and asked it to ferry them to the ice dungeon. However, along the way, Tonkii suddenly dived and stopped at an altitude where they could see the ground. There they saw that players were cooperating with the humanoid evil-god-class monsters to massacre Tonkii's kin, the beast evil-god-class monsters. As they were watching the scene, a giant NPC, the andlaquo;Queen of the Lakeandraquo; Urandeth;r, appeared behind them. The NPC explained that the massacre was ordered by the king of the giants, andTHORN;rym, who once threw the Holy Sword Excaliber into Urandeth;r's Spring and caused the world of Jandouml;tunheimr to turn into an icy wasteland. She then explained that if all of Tonkii's kin were slaughtered, she would lose her power and this would allow andTHORN;rym to invade the land of the fairies, Alfheim. To prevent this, Urandeth;r requested the fairies to retrieve the Holy Sword Excaliber from the bottom of the ice dungeon, called andTHORN;rymheimr.
In the near future, a Virtual Reality Massive Multiplayer Online Role-Playing Game (VRMMORPG) called Sword Art Online has been released where players control their avatars with their bodies using a piece of technology called Nerve Gear. One day, players discover they cannot log out, as the game creator is holding them captive unless they reach the 100th floor of the game's tower and defeat the final boss. However, if they die in the game, they die in real life. Their struggle for survival starts now...