A retail listing for the Xbox 360 version of No More Heroes: Heroes' Paradise in Japan suggests that it will more than likely carry a CERO Z rating (mature) when released in February.
This is because it's the North American version, which still has "bloodshed" intact. With such a strong rating, it is not likely to be carried on normal retail shelves.
PS3 versions probably won't get the same rating, as it's the censored version originally released in Japan.
If this sort of thing interests you, Joystiq has more on it here.