Zerosky
And you have given no basis for why he is capable mastering this technique? I mean why some psychotic 'samurai' was capable of mastering something that even cultivators with superior bodily and mental capabilities can't. And from the description he seemed a rogue and Warriors in japan without Masters are called 'Ronin' not samurai.
So why is this art dangerous? And you are telling just a measley mortal samurai was capable of mastering something that even high level cultivators can't? Is he someone like William(Nioh) if that was it I could accept the fact but how? What are the ranks of Cultivation? Are samurais some elite swordsman or something no they are just soldiers since by your definition all soldiers are elite of the elite.