While I'm more into tools than dedicated weapons, I'll throw out a couple of comments:
The chiruwa handle is likely easier for the kamis to make. They make scissors and bancharos (axes), so using a drift or the like to forge a loop/ring should be known to them. What kind of fairing/tapering of the scales is needed needs to be addressed. Balance/weight is an issue, especially since the ring limits thinning the tang towards the butt as is done on the JKM-1. It wouldn't be as light and quick as a partial tang. Dunno if that matters for this type of weapon, which I imagine in my ignorance has sort of a surprise, one-try sort of use.
Making the ring in horn or wood would probably require them to drill a ring of holes with the electric hand drill, and then lots of filing to complete. I think it would take longer, and there could be a significant failure rate.
Think of the consequences if a crack develops in a horn or wood ring. Big, big bummer. No superglue fix for that. Cosmetic repair, but not functional.
Wild hair idea: How about a pinned partial tang blade and pinned partial tang pommel ring?
One pin should be enough, at least for the ring...less leverage on the ring and one's finger is almost certain to go first anway. It will be easier to forge the ring thicker than the blade, and maybe even have an intergral bolster that fairs into the handle. Balance may be better also. More work, but may be worth it.