This is related to the four character types playable in this game: Power-types, Speed-types, Technical-types, and Sky-types.
As soon as you finish the introduction episode, you'll obtain this, as Luffy is a Power-Type by default. You'll come across the differences and why they matter as you continue on with the game, but for the sake of this trophy, the earliest you can unlock it is through doing the first episode with Luffy.