The Straw Hats Pirates, lead by their captain Monkey D. Luffy, docks near an island to get supplies for future adventures, and to drop of a Raccoon named Pato they found drifting at the ocean. The crew gets kidnapped, and Luffy must travel to different islands to get them back.
For those familiar with the One Piece Series, the main story starts right after Punk Hazard arc, and the Coliseum is in the Dressrosa arc. It’s non-canon, and won’t change anything within the series.
This review tells you why the game isn't worth your buy.