Make dashi: Soak kombu in 8 cups cold water for 20 minutes. Bring to a boil and add bonito. Remove from heat, let sit 5 minutes, then strain through a fine-meshed strainer into a large saucepan.
In a small bowl, mix 2 cups hot dashi with miso, stirring until there are no lumps, then stir back into rest of dashi.
Bring liquid to a gentle simmer (do not boil) and stir in greens, bok choy, scallions, and ginger. Once greens have wilted, stir in tofu and let simmer 5 minutes, then divide among bowls and serve immediately. Serve with chili sauce and/or sesame oil, if you like.
Note: Nutritional analysis is per serving; sodium data not available.