Load a saved game file from .Hack//G.U. Volume 1: Rebirth to unlock an email from Yachimada, 5,000 GP, some random items, and three bonus movies (.hack// Roots episode 1 A and B, and previews for G.U. 1 and 2).
After loading a game save from .Hack//G.U. Volume 1: Rebirth in which you killed Doppelganger, you can try to kill a stronger version. Go to Delta Elegand Your Shadow and kill off all the monsters. Then go to any island other than the one with the temple and wait about fifteen minutes. Return to fight Doppelganger. He is much stronger than you and extremely difficult to defeat, even with two teammates. He recovers HP every few seconds. If you defeat him you will get two of three weapons he carries (if you defeated him in Volume 1) Heine's Invasion (twin blade), Heine's Shadow (broadsword), and Heine's Zero (scythe). Each are level 51 and are the most powerful in the game.
Antares' member address:
When you go to the crowning ceremony, talk to Antares twice and he will give you his member address.
Easy arena matches:
After unlocking the Divine Awakening in the story, just play defensively using counterattacks until your Moral gauge is full. Once full, use it to USUALLY kill the opponents with one shot.