From the introduction:
Everyone who enjoys a show, game, movie or really any content, often wishes to be able to go into their world - wondering what kind of character they'd be, or what powers they would have. This was extra true to us for the manga & show One Piece! Dungeons & Dragons is often a medium for people to live life as a hero, to escape a mundane reality. We wanted to expand that feeling by allowing you to escape into the GREAT PIRATE ERA. To make your own character in the One Piece world and experience the kind of story you've wanted for yourself in this exciting world. Will you be a goofy yet strong pirate like Luffy? Or will you seek out the devil fruits like Kaido? Maybe cracking down on unlawful pirates like Garp is what you're after? Use this as the foundation to seek your own glory!