Chouna shiage: Japanese adze finishing

I'm glad it's a small project, because that looks like a lot of work!

This finish work is very attractive. To my eye it's finish surfacing for timber work. Makoto Imai has several pieces in his gallery. 

https://makotoimai.com/about/

Here is a blog post about chouna shiage from Jon Billing, an American working in Japan, with his experience. He addresses your point about about it being used traditionally for timber framing but he is experimenting with using it for furniture and other smaller work. 

https://www.bigsandwoodworking.com/chouna-shiage-adze-finishing/

i live in a town in the northern part of california,  where makoto had established himself as a teacher on his homestead - i believe it was in the 1990's. am told that people would come to live here for a bit, work with him, and learn timber framing techniques. although i never knew him, i met several folks who worked with him. most of the structures are now in pretty bad shape -many years of winters and no one taking care of the place.  i was told that he left here to move further north to a more consistent moderate climate - because the summertime dry heat affected his wooden tools. he left quite a bit of material.
several years ago a woman who was tasked with looking over his place, cleaning it up, getting ready to put it on the market began to sell off what was left.
here's a partial list of material i was able to get -
3 pieces of clear vertical grain doug fir - 3" thick x 22" wide x 18' (yes feet) long - not a knot
several 11" x 11"x 12' - clear western red cedar beams
many 2x 6 x 12' - clear doug fir.
and similar sized clear port orford cedar boards.

it was a treasure trove

after i brought boards home and lived with them for a while, i looked him up and emailed him telling him what a pleasure it was to get the material. he told that the timbers had been cut in the coos bay, oregon area. he was appreciative of the contact and liked that the wood was being taken care of and used again.
just wanted to share a story
jc