One Piece: Grand Adventure Cheats for the GameCube

Buggy:
Reach the "Top Pirate of the Island" rank to unlock Buggy as a captain in Grand Adventure mode.

Chaser:
Reach level 15 with him in Chaser's adventure, then win a battle using him.

Chaser (Smoker):
Get the "Top Pirate of the Grand Line" rank to unlock Chaser (Smoker) as a captain in Grand Adventure mode.

Crocodile:
Get the "Top Pirate of the Continent" rank to unlock Crocodile as a captain in Grand Adventure mode.

Eneru:
In Adventure mode as Crocodile, get Eneru as an ally in the Jaya area. Then, win a battle using him.

Kuina:
In Adventure mode as Chaser, recruit Kuina in the ship graveyard. Then, defeat Zolo using her in Alabasta.

Mihawk:
In Adventure mode as Chaser (Smoker), get Mihawk as an ally. Then, win a battle using him.

Mr. 2 Bon Clay:
In Adventure mode as Crocodile, get Mr. 2 Bon Clay as an ally. Then, win a battle using him

Nico Robin:
In Adventure mode as Luffy, get Nico Robin an ally. Then, win a battle using her.

Ohm:
In Adventure mode as Crocodile, get Ohm as an ally in the Jaya area. Then, win a battle using him

Shanks:
In Adventure mode as Buggy, get Shanks as an ally. Then, win a battle using him.

Trace (Ace):
In Adventure mode as Buggy, recruit Trace in Drum Island. Then, win a battle using him.

Ussop:
Defeat the final boss in Adventure mode as Luffy, Buggy, Crocodile, and Chaser in any order.

Zeff:
In Adventure mode as Chaser, get Zeff to level 15 and use him once in battle.

Support characters in Grand Battle mode:
Use a support character for three battles in Adventure mode, and they can be used by any character in Grand Battle mode.

Versus mode passwords:
Enter the following case-sensitive passwords to unlock the corresponding level 100 character in Versus mode.