Wolverine set about chopping bits off that guy who killed Mariko. He came back once a year with no other purpose than to chop off another of this guy's fingers. As time went by the guy's face got disfigured pretty badly...
I found this totally unacceptable as a side of wolverine's character. Sure he will kill and he may even have some history of torturing for info, but this was something else.
I hope this never comes back to the surface.
It's been referenced a few times since. There was even a pretty cool storyline about it in Wolverine #175. I don't get the Matsuo (Or however you spell his name.) character at all though.