In a flashback, on September 14, 2025; Sinon, who had accidentally fallen down a trap chute while navigating a dungeon below SBC Gurokken, discovered a boss-class monster and decided 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, thus, by conserving her ammo and accurately hitting the boss's weak spot, she was eventually able to defeat it and acquired a new sniper riffle, the PGM Ultima Ratio Hecate II.
After Sinon successfully attacked the first target of another squadron for her own's, she attempted to snipe the second target, but that giant man named "Behemoth" manage to dodge the bullet, took out a heavy machine gun, which was hidden under his cloak, and started fighting back with its overwhelming power which cornered Sinon and those in her squadron. But in the aftermath of battle Sinon emerged victorious even if her left leg was cut-off in the process.
Meanwhile, in Alfheim, Kirito planned to tell Asuna about something.