Defeat the final Boss on Island 5 to unlock the Hard difficulty.
Defeat the final Boss on Island 5 to unlock New Game+ mode. This will also create a saved game file for One Piece Unlimited Cruise: Episode 2.
Read the monument on the last island to unlock Survival mode.
Successfully complete the game, then start a New Game+ on the Hard difficulty. Open the treasure chest on the Sunny with the key to the lockers. Go to girl's room to change the costumes of your characters.
Successfully complete all 50 rounds in Survival mode. A chest with a certificate will appear. Brook, Nami, Robin, and Usopp can now perform a special combined attack.
Successfully complete the indicated task to unlock the corresponding character in Versus mode:
Aokiji: Defeat Aokiji on the Normal difficulty.
Arlong: Defeat Arlong in Survival mode.
Calgara: Defeat him in Round 20 of Survival mode.
Enel: Defeat Enel on the Normal difficulty.
Evil Guardian: Defeat Evil Guardian in Survival mode.
Krieg: Defeat Krieg on the Normal difficulty.
Kuma: Defeat Kuma on the Hard difficulty.
Kuro: Defeat Kuro on the Normal difficulty.
Monster Point Chopper: Defeat Monster Point Chopper in Survival mode.
Moria: Defeat Moria on the Normal difficulty.
Nightmare Luffy: Have an axe on Island 1. Use the cannon on Sunny, and shoot yourself to the center of the peak. Find four stairs on the right, and use them to go up. There are three bamboo trees on the right-hand side. Dig there to find the treasure chest that unlocks Nightmare Luffy. Alternately, defeat Nightmare Luffy in Survival mode.
Spandam: Defeat Spandam on the Normal difficulty.
Wapul: Defeat Wapul on the Normal difficulty.
Final Boss: Defeat the final Boss on the Hard difficulty.