In a bowl, combine ketchup, soy sauce, Worcestershire sauce, rice vinegar, sugar, Dijon mustard, minced garlic, and grated ginger.
Whisk the ingredients together until the sugar is dissolved, and the sauce is well combined.
Taste the sauce and adjust the flavors according to your preference. To increase the sweetness or saltiness, you can add extra sugar or soy sauce.
To allow the flavors to melt together, let the sauce sit for at least 15 to 20 minutes.
Serve the Katsu sauce alongside your favorite dishes, such as chicken or pork katsu.