Ehhh, in general, crossovers (especially anime crossovers) generally don't work that well. It can be difficult to make characters from one setting mesh with another stting that doesn't share its same rules and norms. Not to mention a DBZ-esque combat show like One Piece, where all the characters have wierd (often overpowered) supernatural abilities.
It also seems like you're thinking about dragging in canon characters as well, which opens up a whole new can of worms.
It may be best to make a Felarya story from the ground up, with your own characters, instead of trying to bring in a whole other setting (especially an anime setting) and trying to force it to fit.