Sword Art Online: Project Alicization, Vol. 3 (manga)

A year after Kazuto and Asuna escaped from Aincrad, the deadly setting of
Sword Art
Online, they're still coping with the aftermath as they try to
recover from the
harrowing experience. Meanwhile, there's a new VRMMO game
sweeping the world's
gamers--Gun Gale Online. When a mysterious player who
calls himself "Death Gun"
claims to be responsible for real-world deaths,
Kazuto (aka Kirito) is recruited to enter
the game to investigate, bringing
an end to his hard-won peace!