hack//Roots is the prequel to the .hack// videogames. It follows the story of Haseo a member of the Twilight Brigade guild. In the year 2015 the C.C. Corp’s building was burned down, and with it most of the data for “The World” was lost. By mixing the remaining data with that of another game, the C.C. Corp was able to create the game, “The World: R2?, unlike the games before this game allowed player versus player combat. The anime starts when Haseo logs into The World R:2 for the first time and falls victim to the PKers that reside within. He is saved by Ovan, which prompts him to join the Twilight Brigade.
The Twilight Brigade members are on a mission to find the Key of the Twilight, however, the TAN guild opposes. Their current mission is to find the 6 virus cores before TAN does, and Haseo has 2 of them, how will he escape from the TAN Guild, and find the Key of Twilight, which might be the answer to everything.