Place 4 cups of water in a medium pot, along with the scallops.Cook for about 20 minutes, or until tender, on a medium heat with lid on.
Lower the heat, and add dashinomoto, soy sauce, sake, mirin and kelp. Turn the heat to medium and when it boils, add the cornstarch slurry. When the soup thickens, add the beaten egg, and stir until the egg is done. Turn the heat off and add the green onion. Serve hot.
Notes
Adjust the seasoning as you go along. Add more liquid katakuriko, as desired thickness of texture to your liking.