Is there an online one piece game?
One Piece Online is a free-to-play MMORPG. It utilizes an instanced, automatic turn-based combat system, with the ability to recruit a multitude of different NPC characters from within the Anime and Manga series. The game utilizes a completely instanced world with no ability to explore.
Is there a RPG One Piece game?
One Piece: Romance Dawn should be much better than it is. A turn-based RPG that goes through the manga's story arcs up until the timeskip, Romance Dawn features a decent combat system that could have served as the basis for a respectable romp through Oda's world.