Sword Art Online 15 (light novel): Alicization Invading — Reki Kawahara

In an effort to discover the truth behind Death Gun, Kirito has entered the Bullet of Bullets tournament in Gun Gale Online, and 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. Lives are on the line once again as Sinon is forced to face her own past--but can Death Gun's bizarre rampage be stopped in time?