Note: This game is also titled .hack G.U. Vol. 3: Aruku Youna Hayasa De.
To obtain the strongest equipment in the game, you must have all Doppleganger items from .hack G.U. Vol. 1 and .hack G.U. Vol. 2 and defeat Doppleganger two times in .hack G.U. Vol. 3. After the second time you defeat him, he will drop the armor "Other Self" and the accessory "Shadow" which are level 150, but the best items in the game.
Successfully complete the game and save when prompted. After the credits, you will have access to the Forest Of Pain.
Successfully complete the Forest Of Pain by reaching floor 100 and defeating Cernunnos.
Defeat Doppleganger two times to unlock DG 0.
Kill all chaotic PKs, then look at the BBS. Natsume should appear in a battle zone in any area.
Defeat Doppleganger two times to unlock Other Sel.
Defeat Doppleganger two times to unlock Shadow.
Reach Floor 50 of the Forest Of Pain.
Obtain the armor customization item Indulgence, which takes damage and converts it to GP damage. Give it to Zelkova, and he will not take most damage because he has 99,999,99 GP.
When playing the steam bike missions and you are about to tag a King Chim Chim, press Select, then press Circle. If done correctly, you will either get three King Chim Chim or finish the race which will give you an easy first place.
Go to an area with the second word "moonflower's" (no matter what, you will suprise attack him) and the third word "moonlight" (no matter what, he will show up). After you find Doppleganger, suprise attack him. Note: This will not hurt him, but will knock him off the wall and to the ground. When he gets up, cast Vak Don on him. Until you do this, he will not take damage. Have Curse and Sleep on your weapon's to keep him from regenerating health and sleep as well as holding him still. Also, have a party of maxed level Haseo, Kite (because he cannot be knocked down), and Balmung. Set them both to Rage or Free-Will.
Go to an area with the second word "moonflower's" and the third word "moonlight". When you find Doppleganger, he will look at you for a moment and then walk around in circles until you press X and surprise attack him. Note: If Doppleganger is close to monsters, run away and warp to a different area with the same second and third word. Otherwise, the monsters will find you and trigger a battle with the Doppleganger and the monsters.