It has not really concordance into the One Piece series and all you see is mainly a lot of charachter that luffy and his crew met in their adventure.
Apart from that, the story and the bad guy is rather negligible.
Without spoilers into a speed abstarct, the crew come into a festival full of pirate. In their trek, they meet a lot of character they have seen before.
The bad guy called Bullet made his apparence. Because of his past, he want to fight everyone to prove that he is the stronger and the one who deserve to be the King of Pirates.
After that, it is a succesion of fight and action until that bullet is defeated.
Being a person who really love One Piece, this film is pretty exciting. But it has nothing to do with the One Piece series storyline. And because of all character present, you cannot see this film separatly of the series.
