I believe I have narrowed down the identity of this unusual Japanese soybean to 2 possibilities, either Kura Hira Mame (black flat soybean) or Gangui Black Soybean, which loosely translates to “goose-bite black bean”. Both beans are very similar in appearance and it is difficult to make a determination. Both have somewhat similar uses, and both are traditional Japanese varieties. Here are the descriptions for both taken from a Japanese website. The “google” translation from Japanese to English is a bit awkward :
Kura Hira Mame- “Black plain beans are a kind of black soybeans, but unlike general soybeans, they are round and flat, and are slightly larger and shiny than black beans. It is a traditional bean that has been made for a long time and is eaten locally as black beans for the New Year. It takes a lot of time and time to cultivate, and the yield and fruit size varies, so the number of farmers who are planted is decreasing. Ripe black peas are said to be sweet and have a good taste, but the edamame is also delicious and delicious.”
Gangui Black Soybean- “Ginger bean is a kind of black bean that has long been rooted in the Tohoku region. Mature beans are rounded, but they are flat like bean beans. In addition, there is a cocoon in the middle, and it is called a gorgeous bean because it looks like a migrating bird wing. In Iwate, the main production area, cropping has flourished since the Taisho era, and it was said that it had a good reputation as being shipped to the Kanto region. It seems that it was also called “Daikoku Bean” because of the large income source from this bean, but it seems that it is not suitable for mass production because it takes time and labor for harvesting and sorting. In local Iwate, gluttonous beans are considered to be the food of the Hare Day, and are eaten during the New Year and celebrations. Recently, natto and tofu have also been made using gorgeous beans.”
This soybean grows to a height of 3 – 3 1/2 foot tall and matures 120 – 130 days from direct seeding in the spring. This is also a very productive bean with good yields.