Lu Hua ate the Shadow Fruit, and his ability was to perfectly reproduce all of Luffy's powers.
He has only one mission: to be Luffy's shadow.
Stand behind Straw Hat, follow silently, take action when needed, and disappear when not needed. Don't steal the limelight, don't change key nodes, and don't interfere with Luffy's growth trajectory. After all, there is only one Pirate King, and he is just the shadow behind the man who wants to become the Pirate King.
