Bring Kombu to 200F (93C).
Remove Kombu and save
Add bonito and bring to a simmer
Strain and reserve
Add remaining ingredients
Bring to a simmer and skim
Place stock into 275F (135C) cook & hold oven and let cook for 6 hrs. This can be done overnight just hold at 160F (71C). Strain and season as desired.
Dehydrate reserved Kombu, mushrooms and bonito. Grind and use to season rice