Sword Art Online: Phantom Bullet, Vol. 4 (manga)

"In order to uncover Death Gun's true identity, Kirito prepares to enter the Bullet of Bullets tournament! As Death Gun's newest target, Sinon stands side-by-side with Kirito, ready to overcome her past trauma by defeating their common foe. At long last, it's time for Kirito's showdown against Death Gun! Why and how did all those players die, and who really killed them? Seeking answers, Kirito steels himself and prepares for battle in this thrilling conclusion to the series!"--