Kirito is the protagonist of Sword Art Online. He is a "solo" player, a player who hasn't joined a guild and usually works alone. He is also one of the very few people to have had the privilege to play in the beta testing period of Sword Art Online. His game alias, Kirito, is created by taking the syllables of the first and last Kanji of his real last and first names respectively: (Kirigaya Kazuto). In the real world, he lives with his aunt and younger cousin in a family of 3.

When Kayaba announced the start of the death game, he is surprised, but unlike everyone else, he quickly gets over it and accepts it to an extent. He invited his friend Klein to go with him but Klein had to find his friends in the game. He was invited to join them but he declined as he couldn't take the pressure of protecting them even with his beta testing knowledge of the game.

Kirito tends to use a single handed straight sword. The blade that he uses most often is the Elucidator. Later on, he acquires a second blade called Dark Repulser that was made by his blacksmith friend, Lisbeth.