A year after escaping Sword Art Online, Kazuto Kirigaya has been settling back into the real world. However, his peace is short-lived as a new incident occurs in a game called Gun Gale Online, where a player by the name of Death Gun appears to be killing people in the real world by shooting them in-game. Approached by officials to assist in investigating the murders, Kazuto assumes his persona of Kirito once again and logs into Gun Gale Online, intent on stopping the killer.

In the year 2022, a massive online role-playing game called Sword Art Online (SAO) is launched. With the aid of "NerveGear" technology, players can control their avatars within the game using nothing but their own thoughts. Kazuto Kirigaya is among the lucky few who get their hands on the first shipment. He logs in to find himself, with ten-thousand others, in the scenic and elaborate world of Aincrad. However, in a cruel turn of events, the players soon realize they cannot log out; the game's creator has trapped them in his new world until they complete all one hundred levels of the game. In order to escape Aincrad, Kirito will now have to interact and cooperate with his fellow players. Some are allies, while others are foes. Sword Art Online is not all fun and games: if they die in Aincrad, they die in real life. Kirito must adapt to his new reality, fight for his survival, and hopefully break free from his virtual hell.