Now I know there's a thread for this, but this character is not a pirate and I think he'd fit into One Piece pretty well.
This character is basically a "Devil Hunter", a man whose life is based on hunting down people with Devil Fruit abilities. He'd use a sword made of kairouseki and a gun that shoots bullets made of kairouseki. He'd also have armor made of kairouseki, so basically he'd be immune to devil fruit attacks. Maybe he'd be working for the world government or maybe he'd just be doing it for his own reasons and there'd be a story behind it.
His whole motive could be how the Devil Fruits have have disturbed/destoryed the balance of power that was once in the world, and that by eliminating those who posess the devil's powers, balance could be restored.
Now the only problem is that I thought he'd have to look really similar to Mihawk, and that wouldn't be cool. I'm sure, however, that an original design could be made. I was thinking he'd look a bit like Van Helsing.
Anyway tell me of you approve of this idea.