Kirito has been chosen to be on the list of one thousand beta testers for a closed beta game called Sword Art Online, the first truly Virtual Reality Massively Multiplayer Online Role-Playing Game (VRMMORPG) for the device called NerveGear, and joined the closed beta version of that Game after that.
He thus became among the list of 10, 000 players who have been trapped in Sword Art Online, where he continued to be a solo player for the vast majority of Game, willingly agreeing to the role on the Beater to lower discrimination against many other former beta testers, as well as actively playing Boss battles among the front line.
Kirito temporarily joined up with the Moonlit Ebony Cats guild after aiding them safely evade a dangerous dungeon, but back to be a solo player after a fatal error led to the death of the other guild people. At some point in the Game, Kirito is called as the «Black Swordsman» (黒の剣士, Kuro no Kenshi) as a result of his tendency to wear black equipment.
Near the end of the Game, Kirito joined the Knights of the Blood guild because of losing a wager with its leader, Heathcliff. Kirito eventually ends the Game by defeating the 75th boss and the last boss that also appeared on that floor, thus clearing the Game.
As Asuna along with a small group of Sword Art Online survivors are not logged out from Sword Art Online game in aftermath of that event, Kazuto started to playing Alfheim Online for a Spriggan because of seeing an in-Game screenshot with what resembled Asuna, and for that reason wanting to investigate the issue. After freeing the 300 remaining captives, Kazuto kept playing Alfheim Online, with new management, together with his old buddies from Sword Art Online game, and also new fellow gamers from Alfheim Online.
From here, we know that Kirito is wearing a lot of clothes, so there are lots of version of Kirito you can cosplay too. And maybe you will need Sword Art Online Kirito costume if you want to cosplay him and attend the next anime convention in your city.
Because of a request from Kikuoka Seijirou, Kazuto temporarily transported his Alfheim Online avatar to the MMO game called Gun Gale ONline via The Seed starting to investigate several strange deaths, rumored to be a mysterious player, mentioning himself as Death Gun. Thus, Kirito joined the largest tournament inside Game called the Bullet of Bullets, to attract the attention of the murderer.
In the aftermath of the incident, Kazuto returned to Alfheim Online and continued playing it together with his friends. A couple months later, Kazuto was offered a part-time job to run a test a new FullDive machine called the Soul Translator, nevertheless, unbeknownst to him, he was actually helping which associated with a military project named Project Alicization.