One year after the SAO incident, Kirito is approached by Seijirou Kikouka from Japan's Ministry of Internal Affairs and Communications Department “VR Division” with a rather peculiar request. Kikuoka has asked Kirito to investigate the “Death Gun” incident that occurred in the gun and steel filled VRMMO called Gun Gale Online (GGO).
“Players who are shot by a mysterious avatar with a jet black gun lose their lives even in the real world.” Failing to turn down Kikuoka's request, Kirito logs into GGO even though he is not completely convinced that what happens in the virtual world could directly and physically affect the real world.
Kirito wanders in an unfamiliar world in order to gain any clues about the “Death Gun." Then, a female sniper named Sinon who owns a gigantic "Hecate II" rifle extends Kirito a helping hand.
With Sinon's help, Kirito decides to enter the “Bullet of Bullets,” a large tournament to choose the mos powerful gunner within GGO, in hopes to become the target of the “Death Gun” and make direct contact with the mysterious avatar.
[Source: official English website]