Place the water and shoyu in a saucepan and heat almost to a boil. Reduce the flame to low and simmer 3 to 4 minutes. Turn off the flame and add the wasabi powder. Stir to mix thoroughly and refrigerate to chill.
Cook the soba as package directs, rinse under cold water and drain. Remove the dipping sauce from the refrigerator, mix in the grated daikon and scallions. Place in small individual dipping bowls. Place the noodles in bowls and garnish with nori. Dip the soba into the sauce before eating.
Per serving - 221 calories, 2 g fat (6% calories from fat), 10 g protein, 41 g carbohydrate, 3 g fiber, 0 mg cholesterol, 641 mg sodium