Sword Art Online (SAO) is a Virtual Reality Massively Multiplayer Online Role-Playing Game (VRMMORPG), released in 2022. With the Nerve Gear, a virtual reality helmet that stimulates the user's five senses via their brain, players can experience and control their in-game characters with their minds.
On November 6, 2022, the players log into SAO for the first time, and later discover that they are unable to log out. They are then informed by Akihiko Kayaba, SAO's creator, that if they wish to be free, they must reach the 100th floor of the game's tower and defeat the final boss. However, if their avatars die in-game, their bodies will also die in the real world. One of these players is Kazuto "Kirito" Kirigaya, who was chosen as one of the 1,000 beta testers in the closed beta. Since he had previous experience and knowledge of the game, he felt that he could beat the game easily.
As a result, he set out to beat the game on his own. As the game progresses for two years, Kirito eventually befriends a female player named Asuna with whom he ultimately falls in love. After the duo discover the identity of Kayaba's avatar in SAO, they confront and destroy him, freeing themselves and the other players from the game.
Upon being sent back to the real world, Kirito learns that Asuna and 300 other SAO players have still not awakened yet. Following a clue about Asuna's whereabouts in another VRMMORPG called Alfheim Online (ALO), Kirito also enters the ALO's mainframe. Helped by his sister Suguha Kirigaya, known as Leafa in the game, he learns that the trapped players in ALO are part of a plan conceived by Nobuyuki SugÅ to perform illegal experiments on their minds to put them under his control, including Asuna, whom he intends to marry in the real world in order to take over her family's company. After Kirito foils Nobuyuki's plans, he finally reunites with Asuna back in the real world.