MMORPG

In the year 2022, the Virtual Reality Massively Multiplayer Online Role-Playing Game (VRMMORPG), Sword Art Online (SAO), is released. 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, all the players log in for the first time, and subsequently discover that they are unable to log out. They are then informed by Kayaba Akihiko, the creator of SAO, 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. The story follows Kirito, a skilled player who is determined to beat the game. As the game progresses, Kirito eventually befriends a female player named Asuna with whom he eventually falls in love with. After the duo discover the identity of Kayaba's avatar in SAO, they confront and defeat him, freeing themselves and the other players from the game.

Upon returning to the real world, Kirito learns that Asuna and a small group of SAO players has still not awakened yet. Following a clue about Asuna's whereabouts in another VRMMORPG called Alfheim Online (ALO), Kirito also logs in there. Later it is revealed that they are trapped ALO as part of a plan devised by Nobuyuki Sugō to perform illegal experiments on their minds to learn 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. Helped by his cousin and adoptive sister Suguha, Kirito stops Nobuyuki's plans and finally reunites with Asuna in the real world.

Soon after, Kirito plays another game called Gun Gale Online (GGO) to investigate the mysterious connection between it and deaths occurring in the real world. Kirito, assisted by a female player he meets in the game called Sinon, eventually identifies and exposes the culprits with include some former members of a murderous guild he had previously encountered in SAO.

After solving the murders in GGO, Kirito is recruited to assist in the development of a state-of-the-art game, UnderWorld (UW), which has an interface that is far more realistic and complex than the previous games he had played. In UW, the flow of time proceeds thousands of times faster than in the real world. However, Kirito ends up falling into a trap set by one of the murderers from GGO and wakes up inside the game, unable to log out, with his real self left in a comatose state. As Kirito begins to have his memories entangled with his experiences in the game, it becomes more difficult for him to tell reality and fiction apart. Meanwhile, Asuna, Suguha and Sinon also log themselves into UW in an attempt to help him.