Wash the radish, cucumber, and onion thoroughly and slice them thinly.
Pour 600ml of water into a pot and add kelp (5g) and shiitake mushrooms (10g). Boil for 10 minutes.
Turn off the heat and remove the kelp and shiitake mushrooms from the pot.
Add apple juice (50ml), vinegar (20ml), soy sauce (10ml), stevia (2g), and salt (3g) to the broth and mix well.
Freeze in the refrigerator until cold.
Serve with cooked noodles, cucumber, radish, and egg, then pour the cold broth over to complete.