Add anchovies and dashima to 6 cups of water. Let soak for 20 minutes.
In a large stock pot, bring 12 cups of water to a boil with the korean radish, onion, garlic, green onion, and shiitake mushrooms. Simmer for 20 minutes.
Add the anchovy and dashima water to the pot of stock. Simmer for another 10 minutes.
Strain. Boom. Now you have anchovy stock.
Any leftover anchovy stock can be frozen in ice cube trays, then transferred to a freezer bag for later use. 2 cubes = 1/2 cup of stock.