In a flashback, on September 14, 2025, Sinon, who had accidentally fallen down a trap chute while navigating a dungeon below SBC Gurokken in GGO, discovers a boss-class monster and decides to die while trying to defeat it. To her surprise, the position she chose for her attack was out of the monster's attack range, and thus, by conserving her ammo and accurately hitting the boss's weak spot, she is eventually able to defeat it and acquire a new sniper rifle, the PGM Ultima Ratio Hecate II. In the present day, during an ambush on an enemy squadron, Sinon attempts to snipe a target, but he turns out to be a bodyguard named "Behemoth", who overwhelms her squadron with a minigun. When Sinon and Behemoth are the only ones remaining on the battlefield, Sinon manages to shoot Behemoth with her Hecate while falling from the air, earning her victory in the gunfight, despite suffering severe damage to her avatar. Meanwhile, in Alfheim Online, Kirito plans to tell Asuna about something.
Nearly a year after the Sword Art Online incident, a new VRMMORPG known as Gun Gale Online has taken Japan by storm. One day, as a top-ranked player named XeXeeD appears on a streamed broadcast via his avatar, a cloaked man calling himself and his weapon "Death Gun" fires a bullet at XeXeeD's avatar through a video screen, causing XeXeeD 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 XeXeeD'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 second Gun Gale Online user. As Kirito 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.