Soak kombu pieces in lukewarm water for at least 10 minutes in a sealed container.

Mix kombu water with soba dipping sauce, adjust seasoning, and chill in the freezer for 1 hour.

Grate the radish and strain through a fine sieve to prepare 1 serving. Chop green onions finely.

Boil water in a pot, add a drop of oil, and cook noodles. Add cold water twice during boiling to maintain texture. Rinse noodles in cold water and drain.