Years after the events of the first .hack installment, the popular but dangerous online game "The World" has been resurrected. As Haseo the Terror of Death, players are thrown into his quest for revenge in his search for the mysterious PK (Player Killer) Tri-Edge. This time, players will interact in the real and virtual worlds with fellow "The World" players through various chats, mails, and fully voiced video news clips. Together with Haseo's virtual partners, login to challenge and solve the mysteries of this new environment, "The World: R2".

The second series in the .hack franchise, GU features both new and familiar characters, and each chapter of the series is designed to be more distinct from each other than the first .hack quadrilogy.