Sword Art Online: Phantom Bullet, Vol. 1 (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!