Kirito, whose real name is Kazuto Kirigaya, is the main protagonist of Sword Art Online II. His background is marked by tragedy and a gradual withdrawal from the real world. Orphaned at a young age after his biological parents died in an accident, he was adopted by his aunt and uncle, Kirigaya Midori and Minetaka. He was raised alongside his cousin, Suguha, who he was led to believe was his biological sister. This familial situation contributed to his complex personality; feeling like an outsider, he developed a deep sense of guilt and inferiority, particularly towards Suguha, leading him to distance himself from her and from people in general. His refuge became computers and video games, a passion fostered by his aunt's work. By the time of the Sword Art Online incident, Kazuto was a skilled, albeit introverted, young gamer who saw virtual worlds as a preferable alternative to an unrewarding reality.

This preference for isolation defines much of Kirito's personality. He is often perceived as direct, blunt, and sometimes rude, which stems not from malice but from a lack of social experience and a fear of not being able to connect with others. He has a tendency to keep people at a distance to avoid the risk of hurting them or being hurt, a coping mechanism forged from past trauma. Despite this, Kirito possesses a strong, consistent moral core. He is inherently kind and protective, often going out of his way to help those in need, even at great personal risk. He is highly emotional and can be consumed by guilt, such as the trauma he carried from the death of his former guild, the Moonlit Black Cats. While he tries to hide his abilities to avoid unwanted attention, he is incredibly determined and never gives up when he has a strong motivation, especially when protecting the people he cares about.

In Sword Art Online II, Kirito's primary motivation is not self-preservation but obligation and a sense of duty. He is enlisted by Kikuoka Seijiro from the Ministry of Internal Affairs to investigate a string of mysterious deaths linked to the virtual reality game Gun Gale Online, where a player known as Death Gun is supposedly able to kill real people by shooting their in-game avatars. Despite his desire to live a normal life after escaping SAO, Kirito feels compelled to use his unique experience to solve this dangerous mystery and prevent further deaths, showcasing his growth from a solo survivalist to someone who takes responsibility for others.

His role in the Phantom Bullet arc of SAO II is therefore that of an investigator and a fish-out-of-water hero. He logs into GGO, a game where swords are obsolete and firearms reign supreme, at a significant disadvantage. His avatar in this world is a rare M9000 type, which has a slender, androgynous, and notably feminine appearance that often leads other players, including his future partner Sinon, to initially mistake him for a girl. This creates both comedic moments and tactical advantages. His primary role is to uncover Death Gun's identity and methods, which forces him to adapt to a completely different style of combat.

Key relationships heavily influence Kirito's actions in this season. His relationship with Asuna remains the emotional anchor of his life. They are a committed couple in the real world, and while he often tries to shield her from danger by keeping his GGO mission a secret, her unwavering support and emotional warmth are presented as a source of strength for him. A new and pivotal relationship is formed with Sinon, the real name of Asada Shino. Initially rivals and then allies, Kirito and Sinon form a deep bond based on mutual understanding of trauma. He sees his own past PTSD reflected in her fear of guns, and he becomes determined to help her confront it. Through their shared battles, they develop a profound friendship built on trust and respect, with Kirito acting as a steadfast partner who refuses to abandon her to her fears. His familial relationship with his sister/cousin Suguha also continues to be important, representing his connection to the real world and his ongoing effort to repair the emotional distance he created in the past.

Kirito shows notable development during Sword Art Online II. The series moves him beyond the role of a trapped swordsman. He willingly enters a hostile world where he is a novice, which requires humility and a steep learning curve. His journey with Sinon allows him to use his past pain not as a weakness, but as a tool for empathy, helping another person overcome their trauma. This reinforces a theme of his character arc: that his traumatic experiences in virtual worlds, while horrifying, have given him unique insights and strength that he can use to save others. He becomes less of a lone wolf and more of a mentor and partner, actively sharing his burden rather than carrying it entirely alone.

Notable abilities are central to how Kirito navigates the challenges of GGO. His primary weapon is not a gun but a photon sword, a lightsaber-like weapon that most players consider impractical. This choice highlights his signature trait: his superhuman reaction time and sword skills, honed through two years of life-or-death combat in SAO. He possesses the rare Dual Blades skill, though he uses it sparingly. His proficiency with the photon sword allows him to deflect automatic gunfire and close distances against opponents with ranged weapons, defying GGO's conventions. He also carries over his high-level «Battle Healing» skill and a unique «Hypersense» ability that allows him to detect killing intent from other players, a direct result of his life in Aincrad. In the real world, his time in VR has left him with surprisingly effective fencing skills, able to hold his own against the nationally ranked kendo practitioner Suguha, and he is also a gifted programmer and analyst.