Nearly a year after the Sword Art Online incident, a new virtual reality MMORPG known as Gun Gale Online has taken Japan by storm. One day, as a top ranked player named Zexceed appears on a streamed broadcast via his avatar, a cloaked man calling himself and his weapon "Death Gun" fires a bullet at Zexceed's avatar through a video screen, causing Zexceed to suddenly convulse and disconnect. A month later, Kazuto Kirigaya is called to meet up with Kikuoka Seijiro of the Ministry of Internal Affairs' Virtual Division, who reveals that Zexceed's user was found dead of acute heart failure a few days after his avatar was shot, also showing evidence of a similar case involving the death of a GGO user. As Kazuto states his doubts that a game could cause someone's heart to fail, Kikuoka, believing Death Gun is specifically targeting professional GGO players, asks Kazuto to once again take up the role of Kirito and investigate what is causing the victims to die. Remembering all the people who died in SAO, Kazuto thinks over his decision whilst spending time with Asuna at the park. Meanwhile, in the world of GGO, a sniper known as Sinon is in top form.