.hack

The franchise primarily surrounds an alternate future in which one operating system, ALTIMIT OS[?], is used by all computers in the world due to various computer viruses (in particular, one named Pluto's Kiss[?]) that crashed the internet in the mid-2000's. ALTIMIT OS is now the only major operating system in the world due to its stability and the difficulty found in crashing the system.

The primary focus of the franchise however is the popular MMORPG The World, which has over one million users upon its launch. The series focuses, however, on a particular set of incidents termed The Twilight Incident in which multiple users were forced into a coma while playing the game. Most of the stories surround an AI named Aura (アウラ) or various other anomalous AIs.

The four initial storylines of the franchise were:

• .hack//SIGN, an anime series surrounding the character Tsukasa (司) and his inability to log out of The World.
• The .hack (games), a set of four video games for the Playstation 2 that follow the story of the .hackers Kite (カイト) and Black Rose (ブラックローズ) and their attempts to find out what caused the sudden coma of Kite's friend, Orca (オルカ).
• .hack//Liminality[?], a set of four DVD OVAs included with the games that follow the story of Mai Minase, Yuki Aihara, Kyoko Tohno, and ex-Cyber Connect 2-employee Junichiro Tokuoka as they attempt to find out what is causing the comas.
• .hack//Tasogare no Udewa Densetsu[?], a manga series (that later became an anime series) following the player characters Rena (レナ) and Shuugo (シューゴ), as they win a mysterious contest that earns them the same character models as the legendary .hackers Kite and Black Rose.

Other storylines of the franchise that were created later were:

• .hack//AI Buster[?], a novel detailing the story of Balmung (バルムンク) and Orca (オルカ) and the adventure through which they became the famous Descendants of Fianna.
• .hack//Another Birth[?], a novelization of the .hack games.
• .hack//Zero[?], another novel that is a sidestory that supposedly deals with the .hack//SIGN character Sora.