Sword Art Online 6 (light novel) - Phantom Bullet

READ THE NOVEL THAT IGNITED THE PHENOMENON!
In an effort to discover the truth behind Death Gun, Kirito has entered the Bullet of Bullets tournament in Gun Gale Online. Both he and Sinon the sniper girl have made it to the finals, and the reality of what they discover is stranger than anything they could've prepared for. As Sinon is forced to face her own past, lives are on the line once again, and Kirito struggles to connect Death Gun to events in the original SAO game--but can Death Gun's bizarre rampage be stopped in time?