Macha is the cat character that appears in .hack//SIGN and other .hack series. Although she appears to be a typical hacker or Vagrant AI, she is actually an alternate form of the Sixth Phase Macha the Temptress. She lures Tsukasa to a secret area, where Morganna can then manipulate him. After the events of SIGN she takes on the form Mia who resembles an older version of herself dressed as a warrior, and goes on adventures with Elk to find aromatic grass because Elk resembles the boy in her dreams(Tsukasa) who gave her aromatic grass in the first place.    In .Hack//GU Endrance(an adult Elk) has the power to summon her true form into battle.

It is the year 2017, and the stakes have gotten even higher in the massively multiplayer online game The World--now The World R:2, a dangerous place overrun by player killers, where lawlessness abounds. The PKK Haseo, known as "The Terror of Death," is a fearsome foe who punishes those who want to slay other players. But things have gotten personal as Haseo tries to track down the killer Tri-Edge, who has threatened the real life of his friend Shino... (Source: Tokyopop)

In the epic prequel to .hack, the avatar Albireo is a solo adventurer in The World, the most advanced online fantasy game ever created. When he comes across Lycoris, a strange little girl in a dungeon, Albireo wonders if she's simply nothing more than a bug in the system. As the two journey further into The World, Albireo watches Lycoris turn all of the rules of The World upside down. Slowly, he comes to realize that she may hold a very deadly secret--a secret that could unhinge everything in cyberspace...and beyond! (Source: Amazon)

While the original four .hack video games followed the tales and travels of Kite, these books tell the story all over again, from the view of Akira Hayami, also known as BlackRose in The World. When her younger brother, Fumikazu, falls into a coma while playing The World, Akira decides to figure out why it happened, and launches herself into the most exciting, and dangerous, journey she will ever have to encounter. Where she meets the twin blade Kite whose friend Orca has fallen into a coma too. Together they venture to find out The World's innermost secrets meeting new friends along the way who aid them in their journey. (Source: Wikipedia)

"The World" is a massively multiplayer online game played by more than twelve million people across the globe. Within this virtual world Haseo, a PK (Player Killer), continues an endless fight. Everything he does is for the sake of the girl Shino, who back in the real world, is hospitalized by an unexplained coma. However, on finally meeting with his sole lead, a PK called &ldquo;Tri-Edge,&rdquo; Haseo is dropped back to Level 1 by a mysterious power! Can Haseo save Shino now that he has lost all of his abilities? Tatsuya Hamasaki, writer of the scenario for the .hack//G.U. games, now turns his hand to its novelization! 
(Source: Tokyopop)

A young wavemaster, only known by the alias of Tsukasa, wakes up in an MMORPG called The World, with slight amnesia. He does not know what he has previously done before he woke up. In The World, he is suspected to be a hacker of the Crimson Knights, as he was seen accompanying a tweaked character in the form of a cat. Unable to log out from the game, he wanders around looking for answers, avoiding the knights and other players he meets along the way. 
As Tsukasa explores The World, he stumbles upon a magical item that takes the form of a 'guardian', which promises him protection from all harm. Subaru, the leader of the Crimson Knights, along with several other players who became acquainted with Tsukasa, set out to investigate why Tsukasa is unable to log out, and attempt to get to the bottom of the problem before it gets out of hand. 
[Written by MAL Rewrite]