Prepare 320g (1 yam) of nagaimo. The skin is edible, so don't peel it. To make the skin easy to eat, stick a fork in it and char the entire surface over a stove burner. This burns off the hairy roots and makes it much easier to eat, and it makes the finished marinade many times better.
Nagaimo (Japanese mountain yam) 320g (1 yam)