One of the reputed virtues is that it makes bruises that do not heal easily. I don't have any, so I can't make a weapon to check this with. Otherwise, a wood for weapons should have shock resilience, some resistance to excessive denting, and be moderate to somewhat dense. When it breaks, it should split apart without splintering and creating tiny projectiles. For most arts, Japanese white oak (shiro kashi, a live oak) fit the bill. Most likely, arts used what they could obtain easily in their natal area. Ryū lore has the foundation on the north coast, but in the late Edo it was centered in Wakayama and Saitama. I wonder if there is forestry information in English that describes the woods harvested in those areas (of course it exists in Japanese, and I'm sure Prof. Totman knows exactly where to find it!).