Sword Art Online: Phantom Bullet, Vol. 3 (manga)

"With the prelims over, it's time to head into the main event--the Bullet of Bullets tournament. But this fun free-for-all has turned into an IRL death match when a member of SAO's Laughing Coffin raises the stakes. Can Sinon and Kirito figure out who Death Gun is before it's too late?"--Back cover.