1/2 cup soy sauce
1/2 cup mirin
1/4 cup sugar
1/4 cup sake
Combine soy sauce, mirin, sugar, and sake in a small saucepan
Heat over medium heat
Stir until the sugar dissolves
Bring to a gentle simmer
Reduce heat to low
Cook until the sauce thickens slightly, about 10 to 15 minutes
Remove from heat
Let cool before using
Store in an airtight container in the refrigerator