Since the fans of One Piece are in love with pirates, I would like to suggest you a soundtrack to listen as a background during Luffy's &co adventures.
There's a German Metal band from the 80s called RUNNING WILD.
They're basically known as the first (and only) PIRATE METAL band.
They play classic/speed/power metal but with a certain vibe that takes you into a world lead by pirates.
Also the lyrics of the albums are based on pirate life and on famous pirate's adventure.
Just to name a few titles:
Under Jolly Roger
Death or Glory
Riding the Storm
Just give them a try and let me know your impressions, you can find something even on youtube