Bring 3 cups of water to a boil in a small saucepan. Add Dashi Moto Soup Stock Base (1 package), Light Soy Sauce (1/3 cup), Mirin (1/4 cup), Granulated Sugar (2 tablespoon) and Rice Vinegar (1/2 teaspoon). Let simmer over medium-high heat for about 5 minutes.
Add Bonito Flakes (1/4 cup), let simmer for another 5 minutes.
Let cool, then chill in refrigerator.
Prepare the Soba Noodles (12 ounce) according to the directions on the packaging.
Strain the noodles in a large colander, then rinse with cold tap water (as cold as possible) for about a minute. Make sure all the noodles are cold.
When the noodles are cold, let it dry for a few minutes, then store in the fridge under plastic wrap until ready to serve.
Garnish with shredded Nori Sheet (1 sheet) and Scallion (1/2 cup). Serve with the chilled broth and enjoy!