This kombu- and bonito-based broth is essential to many Japanese dishes. It's best to use it the same day, but you can store it in the refrigerator for up to two weeks, or you can freeze it.
In a pot, combine the water, ginger, mushrooms, garlic, kombu, and mirin and bring to a light simmer. After simmering for 45-60 minutes, add the soy sauce and sake.
Add more soy sauce, to taste (the broth should be on verge of being salty when warm since it will taste underseasoned when cold). Add the bonito and remove from the heat. Steep for 45 minutes and strain.