One look and these looks like chinese Fish Balls!
I saw these type of Wagashi when I was living around the area of Kyoto, Japan but never got around to try them. Kyoto is a beautiful place, blending the old and new with serene temples, back streets full of old traditional shops selling potteries, ceramics and also food, traditional sweets or modern horseradish/Wasabi flavored ice cream.
There is no flavor in these balls itself which are made of brown rice flour together with glutinous rice flour and the black sauce which is made up of equal parts of soy sauce, sugar and mirin (Japanese sweet seasoning) imparts the hint of dark heavy syrup sweetness into it.
The addition of brown rice flour to the glutinous flour reduces the chewiness texture and produces a firm middle with a slight chewiness on the outside layer of the dango. The making of the dango balls took only 10 minutes and the cooking of the sauce around 10 mins too. The only thing is the coating part which got a bit messy as the sauce thickens when it cools. Overall, these dango were fun to chew on as a light snack with no trace of fat at all but I would buy a daifuku if both were available.