Lord Sinister, One Piece takes place in a world that is mostly ocean with many islands. The 'One Piece' itself is a mysterious treasure left behind by the late great Gold Roger, King of the Pirates. The main characters of the show are the Straw Hat Pirates, led by Monkey D. Luffy. Luffy has eaten a strange fruit that gives him the power to stretch his body like rubber, but takes away his ability to swim. Luffy's dream is to become the next King of the Pirates, so he sets out, gathers a crew, and has all sorts of battles with other pirates, and the Marines (who enforce the laws of the world government).
I LOVE One Piece. It was one of the first mangas I started reading, and the crazy abilities, the characters, and the insane foreshortening on the battle scenes just went completely beyond anything else I'd seen. I still read the new chapters when I get the chance, though I feel the anime has gone kinda wonky. All the characters have giraffe necks.