Put mirin in a sauce pan and heat. Add soy sauce and dashi soup stock in the pan and bring to a boil. Stop the heat. Cool the sauce. Boil lots of water in a large pot. Add dried soba noodles in the boiling water, gently stirring noodles with chopsticks. Turn down the heat to medium. Boil soba noodles, following the package instructions. It usually takes a couple minutes to boil soba. If it’s necessary, add a little bit of cold water in the pot to prevent overflowing. Drain and cool the noodles in cold water. Gently wash noodles with hands and drain well. Divide soba among four serving plates or zaru. Divide dipping sauce among four small cups. Put toppings on small plates and serve them on the side of soba.