The main protagonist of Sword Art Online, Kazuto, who uses the portmanteau "Kirito" as his character name, is a "solo" player who has been branded a "beater" (a combination of beta tester and cheater) by the players in Sword Art Online. When Kayaba announces that the players of SAO can no longer log-out without clearing the game, he quickly overcomes the shock. He power-levels to improve his odds of survival in the game and emerges as a frontline floor-clearer known as the Black Swordsman (黒の剣士 Kuro no Kenshi?), during this time Kirito experiences great trauma following the destruction of a small guild he had joined for some time, causing him to avoid guilds until he was forced to join the Knights of the Blood Oath. It is later revealed that he possessed the unique «Dual Blades» skill for being the player with "fastest reaction time" as well as the player that will supposedly beat the 100th floor boss. During his 2 years of being trapped in SAO, he fell in love with a female player named Asuna and even went as far as marrying her in-game.
After the Sword Art Online incident, 300 people have yet to wake up, including Asuna. Kirito receives a picture from another virtual reality called Alfheim Online, in which Asuna was trapped in a cage on the legendary World Tree, which no ALO player has ever reached directly. Kirito decides to get a copy of the game and rescue Asuna nonetheless. Shortly after joining ALO, he befriends another player called "Leafa" (who is actually his cousin Suguha). Leafa helps Kirito grasp the game and offers to help him reach the World Tree. After a long journey and many adventures, Kirito manages to reach the World Tree and overcomes its obstacles to reach the top. He rescues Asuna and discovers Leafa's true identity. As ALO and SAO share the same game engine, among other features, a bug allows Kirito to retain most of the skills and money he obtained in SAO upon playing ALO with the same NerveGear, already beginning his journey with an advantage over other players. Despite this, he ends up being forced to discard all of his items (except the one containing Yui, which reformats itself as a navigation pixie), as they were not recognized by the system. Kirito obtains the game's administrative ID from Kayaba's digital ghost during his battle with Oberon, granting him full control over the game's systems. Kazuto enrolls at the SAO Survivor School with Asuna and the other heroines in the real world.
He is later asked to register in Gun Gale Online in order to investigate real life murders that are somehow linked with assassinations in-game. It is soon revealed that the murders are committed by ex-players from Sword Art Online, who were part of a player killing guild known as Laughing Coffin. His actions result in the capture of two out of the three culprits. The last member escapes and is not heard of until the events of volume 9 and is responsible for an attempted murder of Kazuto.
In the Alicization Arc, he has been assisting in the development of the fourth generation full dive interface, Soul Translator, by testing its thought acceleration functions. However, he has no memory of what he has been doing as a result of his memories being suppressed, voluntarily, by the system. He is attacked and poisoned by Johnny Black (The third culprit who escapes) in the real world and wakes up in UnderWorld with his memory of playing the game erased. He meets up with Eugeo and helps him out of some tough situations, during which he partially remembers his time with Eugeo and Alice during his "childhood" in UnderWorld. He then decides to aid Eugeo in finding Alice while he searches for a way out, back to reality.
In the real world, he lives with his foster mother and aunt, Midori, and younger sister, Suguha, in a family of three. In fact, he was actually adopted by Minetaka Kirigaya and Midori Kirigaya when he was just a year old, due to his real mother and father dying after an accident, and practice Kendo under his strict grandfather. However, Kazuto did not know this until he discovered the truth at the age of ten, and Suguha, being in fact the Midori's own daughter, was also unaware of Kazuto's adoption and is actually his cousin. This drove him into online playing: quitting Kendo and having a distant relationship with Suguha until his 2-year experience in SAO then makes amends.
Asuna
- Asuna (アスナ Asuna?) / Asuna Yuuki (結城 明日奈 Yūki Asuna?)
- Voiced by: Haruka Tomatsu (Japanese), Cherami Leigh (English)
The main heroine of Sword Art Online and main protagonist of the seventh volume, Asuna is a friend and later to be wife of Kirito and a sub-leader of the "Knights of the Blood Oath", a medium-sized guild acknowledged as the strongest guild in Aincrad. Being one of the few girls that play SAO and extremely attractive, she receives many invitations and proposals. Asuna is a strong-willed, accomplished player known in-game as the "Lightning Flash" (閃光 Senkō?) for her extraordinary fast sword skill.
Later, she falls in love with Kirito and they marry in-game. Towards the end of the SAO arc, she saves Kirito from a killing blow by Heathcliff at the cost of her life. However, her death was only in-game and she is shortly reunited with Kirito shortly after the death of Heathcliff.
Despite the completion of SAO, Asuna remains unconscious and is instead detained in another virtual reality called Alfheim Online. She is forced to play the role of «Titania the Queen of Fairies», with Nobuyuki Sugō, the man responsible for imprisoning her, playing as Oberon the Fairy King. This is done so that Sugō could marry Asuna in the real world, while she is unconscious and thus take over RCT Progress Inc. She attempts to escape the World Tree where she is imprisoned and manages to steal a GM card which she throws out of the window when she hears Yui's voice. Upon being released she creates two avatars for Alfheim, Asuna (being the healer of the team) and Erika (a battle type avatar) and went on to continue living together with Kirito. She enrolls at the SAO Survivor School with Kazuto Kirigaya in the real world after everything ended.
In the real world, Asuna's parents want her to follow in their footsteps. However, after living in SAO and meeting Kirito, she gains a different perspective and looks back on her past with disgust. She officially becomes Kazuto's real life girlfriend and dreams of marrying him and having a family with him in the future.
