Combine dashi stock, soy sauce, mirin, sugar, and sake in a large pot

Add kombu seaweed and bring to a gentle boil

Add cooked soybeans and grated ginger

Reduce heat to low and simmer partially covered for 25-30 minutes

Stir occasionally and add water if needed to prevent sticking

Remove kombu when soybeans are tender and liquid has reduced

Continue simmering until sauce coats the beans

Let cool slightly before serving to allow flavors to absorb