In the near future, after a global computer virus attack, the only online game is "The World."
In .hack//Enemy, two players unleash a horse of monsters from "The World" on their vulnerable opponents. When enough of one player's monster successfully attack, that player wins. Some monsters can even safely hide in a portal, waiting for more and more monster to join in a vicious attack.
As a last line of defense, each player also controls up to thee PCs (player characters) to fight against the opponent's monsters. PCs are chosen from six different classes. Each class has its own special weapons, actions, and abilities.