Focus on this trophy while playing through Dramatic Log; if you still don't have it by the full completion of the Wano Island Arc, you are better off at this point. Once you've completed that log, you'll have the unlock requirements for every character displayed, meaning what characters you don't have will show up with information on how to unlock them in the specific option under the pre-battle screen. There are a few that will require you to play the Treasure Log or needing S ranks, such as Marco, Buggy, and Ivankov, but the majority can be obtained just from the story itself.