Soy has been eaten in Japan since a very long time. It was mentioned even in the Kojiki - the oldest chronicle of Japan, "Record Of Ancient Matters" 712 A.D. Soy is an ingredient for toufu, soy sauce, miso paste. It is less known and less found as sprouts.
In the left part of the photo:
I ate it in nabe and grilled. It takes 4-5 days to reach the appropriate length. In the past, Kanto Moyashi grew about 10 tons of them every day. It is less spread, yet tasty.