Put water and kombu in a pot and let it sit for at least 30 minutes until the kombu softens.
Heat the pot over very low heat for about 10 minutes (for 2 servings). When small bubbles appear on the surface of the liquid, remove the kombu.
Increase the heat and bring the water (kombu dashi) to a boil. Once boiling, reduce the heat to low, add bonito flakes, and let it simmer for 3 minutes.
Turn off the heat and strain the mixture through a sieve lined with paper towels or a cloth (such as cheesecloth). Alternatively, if you don't mind having some fine bonito flakes remaining, you can simply use a fine-mesh strainer. Awase dashi, which combines kombu dashi and bonito dashi, is now ready.
Cut tofu into bite-sized pieces. Thinly slice green onions.
Add the dashi, tofu, and wakame seaweed to the pot and cook until heated through.
Turn off the heat and dissolve miso in the pot using a ladle and chopsticks. Serve in each bowl and top with the green onions.