As much as I adore Kuro, Fuuma can rip down a whole building without breaking a sweat. With his powers restricted, Kurogane might give him a run for his money. They would probably think it was fun because they are dumb like that. No killing though, since Kuro seems to have a pretty strong will to live.
If Fai could have any super power ever, apart from his own, what would he pick?