1/2 cup ketchup
2 tablespoons Worcestershire sauce
1 tablespoon soy sauce
1 tablespoon oyster sauce
1 tablespoon sugar
1 teaspoon mirin
1/2 teaspoon Dijon mustard
Mix all ingredients in a bowl until smooth
Taste and adjust sweetness or saltiness if needed
Serve with tonkatsu, chicken katsu, or other fried foods