When Ichigo first encounters Kenpachi he feels a knife being held to his throat:
Notice the knife is being held by a skeleton.
Kenpachi wears and eyepatch which is traditionally pirate in the sense that do-rags are traditionally gangsta. You could argue that the bells are somewhat piratey too:
His sword has a nautical style hilt and a jagged edge. A pirate sword if I ever saw one:
He's the only captain that's got a tattered robe, when you're a pirate your clothes tend to get pretty tattered: