Successfully complete Event Battle with Luffy, Zoro, Nami, Usopp, Sanji, Chopper, Robin, Buggy, Kuro, Krieg, Arlong, Smoker, Bon Clay, Crocodile, and Foxy. Then, play Event Battle again with Luffy. In the final stage you will battle Aokiji. To unlock Aokiji, you must use your level 2 special.