Whether Yojimbo uses Zanmato depends on other conditions apart from how much you pay him. Plus I think he does it more easily in the PAL version of the game than in the NTSC. I have the PAL version and paid him about 10gil and he used Zanmato on a dark aeon. And there are people who will say that's not possible but all I can say is I did that and it worked.

This thread might have some more information to help you in, I know people were talking about it a lot in there:

http://forums.eyesonff.com/showthrea...t=22160&page=3

I don't know exactly about the conditions and stuff though, sorry.