After escaping Sword Art Online, Kazuto Kirigaya has been living a peaceful life in the real world for a year. However, this peace is short-lived when a new incident occurs in Gun Gale Online, where Death Gun appears to be killing people in the real world by shooting them in-game. The authorities approach Kazuto and ask him to help investigate these murders. He decides to take on his persona of Kirito once again and logs into Gun Gale Online with the intention of stopping Death Gun. Inside, he meets Sinon, a skilled sniper who has experienced trauma. She becomes involved in his pursuit of Death Gun, and they enter the Bullet of Bullets tournament, where their target is sure to appear. Although Kirito is uncertain about Death Gun's true powers, he and Sinon race against time to stop him before he can claim another life. However, scars from the past hinder their progress in this high-stakes game, where the next victim could be one of them. Kazuto puts his life on the line once more in the virtual world to protect others.
Sword Art Online II adapts novels 5 to 8 of Reki Kawaharas light novel series of the same title.The first episode was screened at various special events held in the United States, France, Germany, Hong Kong, Taiwan, Korea and Japan before its television premiere.