Combine the dashi, soy sauce, mirin, and sugar in a small saucepan.

Let the mixture simmer until the sugar is completely dissolved. Remove from the heat and set aside to cool before transferring the sauce to a mason jar.

Warm the tempura dipping sauce and serve in a small bowl alongside your favorite tempura when ready to serve. If desired, grate the daikon radish and squeeze out majority of the liquid. Add a small amount of daikon to the sauce.