Kirito and Asuna take a break at their new home in a secluded village in the 22th floor. As the two of them spend time together, they find a lost girl in the forest. To their curiosity, the girl doesn't have a cursor above her, suggesting a glitch. After taking the girl to their home, she wakes up and claims not to remember anything but her name Yui. Yui, unable to pronounce Asuna's and Kirito's name right, calls them 'mama' and 'papa' respectively. Believing she got lost from her family, Kirito and Asuna decide to head to the Town of Beginnings on the 1st floor to find Yui's relatives and regain her memories before they go back to the front lines. Instead, they find a young woman named Sasha and the children she's taking care of being harassed by the Army for taxes. Asuna attacks their leader until he and the rest of his men run away. As Sasha and the children thank Asuna, Yui tells Kirito she realizes she has never been to the Town of Beginnings before. A mysterious static sound affects everyone before Yui faints.
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...