This dish is inspired the duck dish by Yasuo "Frank" and Hideko Matsuki from Sushi Koto in Fountain Valley. Its not identical as I have forgotten exactly how they prepare it. I believe they actually bake theirs, I pan sear mine.
Ninben Tsuyu No Moto (Seasoning Soy Sauce). If you can't find it its just Dashi and Soy.
I don't have exact measurements of each ingredient. I just go by feel. Just take it easy on the sugar. Have enough liquid to cover the duck breasts.
Sushi Koto serves this as an appetizer. I think it goes well on top of a green salad or even in a sandwich, just serve in crusty French bread, arugula, tomato and a tiny bit of Japanese mayo.
I have yet to try it with wild duck as I didn't manage to get any waterfowl hunting done last season. No bad weather means no waterfowl.