Add 100 ml dashi stock, 4 tsp mirin and 4 tsp Japanese soy sauce (koikuchi shoyu) to a small saucepan and turn on the heat to medium/high. Bring to boil and allow the sauce to bubble for 1-2 mins to burn off the alcohol in the mirin.
Remove the pan from the heat and leave to cool. Once cool to the touch, transfer to a sealable container and refrigerate until it's time to serve.
Serve in individual dipping bowls and add grated daikon, ginger or momiji oroshi to taste.