In light of .hack//legend of the twilight's large amount of sales, the good folks over at Tokyopop decided to translate and publish the popular .hack novels from Japan. At the time of writing there are three different .hack novel series; .hack//AI buster (two volumes), .hack//Another Birth (four volumes), and .hack//Zero.
//AI Buster
Follow the adventures of Albreio and Lycoris in the beta version of 'The World', fragment in the first volume of AI buster. AI buster 2 continues with the story of the AI debugger Albireo as he journeys further into The World. He soon discovers that there is one AI who cannot be killed with his legendary Spear of Wotan. "Crossing the rifts of time, his divine weapon--and Albireo's lonely heart--reach one special girl, called Kamui".
//Another Birth
The Another Birth novels take place during the events of the first four .hack video games. The books plot unfolds through the eyes of one of the games main characters, Blackrose. "In order for Akira to save her younger brother, who suddenly lost consciousness in the middle of playing in The World, she enters The World as the swords-woman Blackrose."