Slice the cucumber into 1-2 mm slices. Peel the daikon radish and chop.
Bring water to a boil. Once it's boiling, add the daikon radish and then the cucumber (in that order). When the water begins to boil again, let the vegetables steam and then blanch in cold water. Drain the water.
Combine with the flavoring ingredients.
Right before eating, drizzle with soy sauce and enjoy.
Story Behind this Recipe
Apparently this is a very popular dish on the kindergarten lunch menu. I tried recreating the dish relying on what my kids remembered about it, and the school lunch menu. Using usukuchi soy sauce retains the vibrant colors of the vegetables. It's lightly seasoned, so you can adjust the flavor by adding more bonito flakes or adding more soy sauce at the end.
This tastes great with just cucumber too. Quickly boiling the vegetables keeps the color vibrant, removes any impurities, and makes it easier to eat. When draining the water, don't tightly wring out the moisture in order to save the delicious texture of the vegetables. My family always uses a larger amount of bonito flakes. It will probably taste best if you top with some at the end.