Kazuto Kirigaya, known by his in-game alias Kirito, is the central protagonist of the Sword Art Online series, including the film Sword Art Online the Movie: Integral Domain, which takes place after the events of the Alicization arc. He was born as Kazuto Narusaka and later adopted by his aunt and uncle, taking the surname Kirigaya. As a teenager, he was selected as one of one thousand beta testers for the first full-dive virtual reality massively multiplayer online role-playing game, Sword Art Online, which used the NerveGear headset to directly stimulate the user's senses. When the game officially launched, he and the other ten thousand players became trapped inside when the creator, Kayaba Akihiko, turned it into a death game where death in the virtual world meant death in reality. Kirito quickly accepted the new conditions and used his prior experience to increase his chances of survival, choosing to play alone to protect other beta testers from discrimination. He coined and accepted the label beater, a combination of beta tester and cheater, to draw hostility away from other beta testers. Throughout his journey, he befriended and later formed a deep romantic partnership with Asuna Yuuki, marrying her within the game and eventually reuniting with her in the real world. Their relationship remains at the emotional core of the narrative, and together they later adopt an artificial intelligence named Yui as their in-game daughter. Kirito is known for his exceptional talent as a VRMMO player, earning him the nickname the Black Swordsman. He wields a single-handed straight sword as his primary weapon, most notably the Elucidator, and later acquires a second blade called the Dark Repulser, forged by his friend Lisbeth. He is granted the unique skill Dual Blades, which allows him to equip and fight with two swords simultaneously, a skill originally designed for the hero destined to defeat the final boss of Aincrad. After escaping Sword Art Online, he learns that three hundred players remain trapped, including Asuna, and enters the virtual world of Alfheim Online to rescue them, uncovering an illegal experiment by Nobuyuki Sugou. He later investigates a series of murders linked to the game Gun Gale Online with the help of a player named Sinon, and is recruited to test an advanced full-dive machine called the Soul Translator, entering a simulated world known as Underworld where time flows a thousand times faster than reality. There, he becomes entangled in a conflict over artificial intelligence and the project known as Alicization, which deeply affects him emotionally and psychologically. In Integral Domain, he and Asuna return to face a new original story set after these events, continuing the exploration of the boundaries between virtual worlds, technology, and human consciousness. Kirito is driven by a strong sense of responsibility to protect those close to him, often taking on burdens alone despite his tendency to isolate himself. Over time, he grows from a solitary player into someone who relies on and fights alongside his companions, maturing through the trauma and loss he experiences across multiple virtual worlds. His key relationships include Asuna as his partner and eventual wife, his cousin Suguha who supports him in both real and virtual realms, and allies such as Agil, Klein, and the artificial being Alice. His abilities combine sharp tactical thinking, rapid adaptation to new environments, and exceptional combat skill, making him a formidable force in any virtual space he enters.