I am sure that hemp was well known in Japan – all those ships needed rigging after all – but do you think that the leaves depicted on this tsuba (see link) are really cannabis?
BTW judging by the centering of the nakago-ana, the maker of the tsuba must have been a heavy user of the stuff...
P.S. note once again how, in typical Catawiki fashion, the material is proudly described as "Cast iron"