Dream Sea was originally conceived by and for Anime Roleplayers looking for less hard-number-comparing to resolve conflicts and special attention to creative ideas rather then plain powerstacking and constant fight scenes. Combat is certainly a part of the game, but designed to be handled in a cooperative-competitive fashion rather then a hostile one.
Set up as an alternate Universe, anything's possible as far as concepts for Characters and Plots goes. The canon's main races are represented with various advantages and perks, while there is an almost infinite diversity of possible Devil Fruit Abilities and Equipment that one can custom-create for their needs and ideas. Technically between those factors, almost any idea can be realized one way or another.
A multitude of locations as well as the popular factions of the story -the Pirates, the Marines and the Revolutionary Army- mean to illustrate and flavor the game towards the OP source material.
While knowledge of and about the One Piece Universe is helpful, it is not required, as the rules and setting are cumulative and inclusive enough to teach you all you need to know. Any Player looking to place a somewhat crazy Character concept into an action-heavy Universe is welcome to have a go.