This is for the American version. First, go to the title screen then hold the R button while entering these codes. (If you mess up entering these codes press start then back to the title screen.) You"ll hear a ding if you entered correctly then release the R and view the costume. Make sure to press the buttons quickly!
Luffys 4th costume- Up ,X, Up, X ,B, A, A, Up
Namis 4th costume- Left, X, Left, X, Y, Y, B, Down
Zolos 4th costume- Down, X, Down, X, B, A, A, Y
Tony Tony Choppers 4th costume- Left, A, Right, X, Y ,Left, Right, B