.hack//G.U. vol. 1//Rebirth
Story
Following the events of .hack//Roots, Haseo has become a ruthless and powerful player. A chance encounter with Ovan leads him to the Hulle Granz Cathedral, where Shino was put into a coma. He encounters and battles "Tri-Edge" but is soundly defeated. Tri-Edge uses a powerful, illegal skill called "Data Drain" on Haseo, which resets his character data to level one. Lacking the strength he once had, Haseo is mistaken for a newbie player by Silabus and Gaspard, who invite him to join their guild, Canard, eventually becoming its Guild Master. During this, he is approached by Kuhn and Pi, two players associated with G.U., a group run by Yata who works for CC Corp, and is investigating AIDA, a bizarre computer anomaly that is appearing in the game.
Yata requests Haseo's help as he is an Epitaph User, and is one of the Eight players who can use an Avatar, the only vehicle to combat AIDA. Haseo agrees on the condition that Yata find Tri-Edge for him, which Yata agrees with. During this, he sees another player playing with AIDA, which appears as a bubbling mass of black dots. During this time he is repeatedly contacted by Atoli, a gentle healer that tries to convince Haseo to enjoy the game and its world more, though Haseo constantly ridicules her for her naivete and ridiculous attitude toward a video game.
By chance, Haseo watches an arena match between Endrance, Arena Emperor, and a challenger, and is startled to see Endrance, the player he saw with AIDA, use an Avatar. Determined to learn more, he joins the arena and eventually defeats Endrance, revealing that his cat is an AIDA program.
After winning, Atoli, on advice from Ovan, finds a Tri-Edge sign, a red carving, and transports to Outer Space, a region outside the normal game parameters, determined to get Haseo to see her as valuable. Realizing she is in great danger, Haseo, Pi, and Kuhn locate her struggling to open a locker. After distracting her, Tri-Edge appears, and is defeated by Haseo. After doing so, the lockers fly open, and an AIDA tentacle pierces Atoli's character.
Source Taken from http://en.wikipedia.org/wiki/.hack//G.U.
.hack//G.U. vol. 2//Reminisce
Vol. 2
After Atoli is rendered unconscious by AIDA, Haseo and the GU staff find themselves trapped inside the game, physically unable to leave or log out, or remove their hardware. Atoli recovers, but is rendered mute, able to communicate only through instant messages. Yata explains that AIDA has copied "The World"'s server, trapping everyone inside to experiment on them. After cracking into the administrative control area, they transfer everyone back to CC Corp's servers, to find only a few minutes have past, opposed to the hours experienced by the players, who are written off as a mass hoax.
Haseo is approached by Alkaid, concerned for Sirius, Emperor of the Holy Palace. Fighting through the Holy Palace tournament, Haseo confronts Bordeaux, infected by AIDA and obsessed with killing Haseo, but is saved by Endrance, whom he rescues from being trapped inside the World. Alkaid is also slain, her player slipping into a coma. After defeating Sirius, they purge him of his AIDA infection.
Atoli is approached by Sakaki, who convinces her that the deaths of Shino and Alkaid, as well as everyone who died on the AIDA server are her fault. The mental stress, as well as an infection of AIDA forced on her by Sakaki, cause Atoli to slide into a depressed fugue, totally under Sakaki's control. Sakaki attacks his own guild Moon Tree, in order to drive Atoli to the point where she will utilize her Avatar to actively support the AIDA infestation in order to control the real world through the Net, using AIDA as a cat's paw. Haseo liberates Atoli, removing her infection, and driving off Sakaki. Tri-Edge, during this time, recuperates, and begins pursuit of Haseo.
Tracking Sakaki, Haseo defeats him after he purposely infects himself with AIDA in a last ditch effort to gain control of the network. Following this, Ovan appears and reveals that he is Tri-Edge, infected in his left arm with AIDA spurs that make the unique Tri-edge sign. Haseo, despondent, vows to pursue and confront Ovan.
Source Taken from http://en.wikipedia.org/wiki/.hack//G.U.
.hack//G.U. vol. 3//Redemption EnD
The final volume of the GU series opens with Ovan reading a book to his sister Aina, also locked in a coma. He is taken over by the AIDA infection in his arm, leaving the area, while Yata is confronted by CC Corp Executives and forcibly removed from the Serpent of Lore Haseo and the rest of the GU members are shocked to find Sakaki, now obviously infected by AIDA, has replaced Yata, after promising CC Corp to remove the threat of AIDA against the greater networks. Sakaki forces Haseo into a PK tournament that is corrupted by AIDA. Haseo has no choice but to fight in the tournament. Haseo and the others go to find Yata to see he is also a Epitaph user and has the avatar Fidechell.
Meanwhile Pi finds ways to talk and get around Sakaki by using outer dungeons, hacked-out world dungeons beyond the systems parameters. The group agrees to participate in the tournament only to end up fighting Sakaki in the end. After the triumphant win over Sakaki, he loses the AIDA infected in him. After the fight reports of a girl in gothic white clothing is seen walking around leading to suspicion. Ovan tracks down Aina who is the mysterious girl and so does Haseo only having them encounter one another. Ovan tells Haseo to meet him at the specific words he gives him and use the outer dungeon to get to him. Haseo goes to the area with Kuhn and Pi to finally find Ovan and finally confront him a final battle.
After the battle and Ovan being Data drained by Haseo's avatar, Skeith, Ovan uses his avatars special ability known as "The Rebirth" and completely resets the Internet almost destroying Haseo's character, and cleanse it of AIDA. Haseo awakens to find himself in a pale room thinking this is his death, only to hear Moon Tree's guild leader Zelkova talking to him and letting Haseo know this isn't the end. Zelkova then hacks Haseo's character to give him another Adept Rogue ability upgrade.
Haseo then comes to find himself in the "Net Slums", a place for hackers and Vagrant AIs to call home, and finds Zelkova there. Zelkova explains to Haseo what happened and that the system has been erased of AIDA and some of the Lost Ones have been recovered, but Shino still remains in a coma. Haseo receives a message from Yata requesting him to come to the Bulwark wall to have him see something. Haseo meets with Yata and Yata explains there is now a bigger threat amongst them now and tells Haseo to look in the chasm before them, to find Cubia. Cubia is the same parameter type boss from .hack//QUARANTINE (one of many references). Yata refers to the Key of the Twilight, and the Epitaph of Twilight being the things to stop Cubia. Yata and Haseo embark for the Hule Granz Cathedral (Delta Hidden Forbidden Holy Ground), to see if they could speak with Aura. As Haseo and Yata arrive Aura sends her guards to confront them first to test them, her guards are Azure Kite, Balmung and Orca. After the fight Aura repeats the Epitath of Twilight poem and the Avatars: Skeith, Innis, Magus, Gorre, Macha, Fidechell, Tarvos, and Corbenik. Haseo realizes that the 8 Epitaph Users ARE the Key of the Twilight and realize that they are the key to defeating Cubia.
Cubia sends out to attack The World after their meeting with Aura. Haseo realizes not all 7 of them can defeat Cubia and sends out a message to all asking to help them in their fight. As Haseo takes the lead to where Cubia is, all guilds and players step up to fight the Cubia Gomoras (Cubia's minions) and help Haseo. Haseo then goes to the outer dungeons to fight Cubia and finish everything once and for all and to save all the lost ones. After the long fight that follows, Haseo receives a message to go back to the Cathedral again, for once Haseo goes there he finds Shino, the one hes always been fighting for to help.
Source Taken from http://en.wikipedia.org/wiki/.hack//G.U.