NHK Video all about Kohya Tofu:
https://www3.nhk.or.jp/nhkworld/en/shows/2054182/
History of Koyadofu. (according to Wikipedia)
In Japan, frozen-dried tofu was developed before frozen tofu. There are two traditional centers of origination of freeze-dried tofu in Japan, including Mount Koya and Nagano.
Mount Koya
It was developed by Mokujiki Shonin, a Shingon priest in the early 1600s during the Edo Period. He encouraged all the mountain temples to make their own tofu after he obtained large amounts of soybeans from the head Shingon temple. The purpose of this was to preserve some of the frozen tofu until the Spring equinox. Firm tofu was left outdoors in the cold windy night to freeze. After it was frozen, it was allowed to stand on shelves in a shed for fifteen days at temperatures below freezing, thawed in warm water and pressed lightly to expel the melted ice, then dried in the shed using heat from charcoal braziers. 
Nagano
Nagano, located to the northeast of Tokyo, was the second center of origination. Freeze-dried tofu was first made during the mid-1500s. It was made by the famous feudal lord and warrior, Takeda Shingen, who developed a new drying process. The purpose was to make nutritious, but lightweight food for the soldiers. Firm tofu was frozen solid on boards outdoors in the snow. It was then wrapped in straw mats and placed in a cold barn for seven days, after which five pieces of tofu were tied together with bits of rice straw, which were then hung from poles, away from the sunlight. After thawing the frozen portions in the day then freezing at night multiple times, the tofu became a hard sponge.
Ukkarimura Tofu is made in Nagano Japan.
Nutrition and health
Koyadofu is high in nutritional value. The way it is produced lets soy protein mature naturally, which helps in the development of new textures, preserving maximum nutritious value. Phytonutrients become more concentrated in it. Freeze-dried tofu serves as a source of protein, iron, and calcium. The protein in koyadofu makes up the fundamental structures of somatic cells. Consumption of this type of tofu lowers the risk of heart disease, diabetes, and obesity. This is why Koyadofu has become so popular for keto, high protein, no carbohydrate diets.