ONE PIECE: PIRATE WARRIORS 4

In the pre-battle screen, if you press R1 or L1 a few times, you'll find there's an option to find the unlockable requirements for some characters. Not all will show up as soon as you look, but as you progress through the game or near their requirements, they will end up appearing. Focus less on this and more on completing your Dramatic Log, for once you've completed the final episode in that, all unlocking requirements will appear on the list. There are a little over 30 characters to unlock, and a few characters require an amount unlocked as well; use that as a tracker if you need to.