In a large bowl, whisk together the soy sauce, mirin, sesame oil, miso paste and sugar until the sugar begins to dissolve and there are no large clumps of miso.
Wrap the tofu in a clean dish towel or several layers of paper towel and twist both ends to secure the tofu. Squeeze and "wring" the towel to drain the water out of the tofu (it's ok if the tofu breaks a bit, it will be crumbled anyway in the salad).
Once most of the liquid is drained from the tofu, crumble it into the bowl with the dressing. Mix to combine and set aside in the fridge.
Prepare an ice bath for the shungiku. Get a large bowl and fill halfway with ice. Add in cold water and set aside.
Wash the greens well. I like to get a large pot out and submerge the greens in cold water and rub loose any residual dirt or sand, switching the water out 2-3 times until the water runs clear.
Cut the ends off the shungiku stems and cut the stems into 1 inch pieces. Cut the leaves roughly into about the same size. Keep the stems and leaves separated for the blanching process.
Bring a pot of water to a boil. Add the sea salt and the shungiku stems. Cook the stems for 2-3 minutes, depending on the thickness (2 minutes for thinner stems, 3 minutes for thicker ones).
During the last 30 seconds of the cooking time, add in the leaves and blanch them until they turn bright green.
Using tongs, drain the greens from the pot and plunge them into the ice bath to halt the cooking process. Keep them in the ice bath for 2-3 minutes until fully cold.
Drain the greens. Using your hands, squeeze as much water out as possible from them and add them to the tofu and dressing mixture.
Toss everything to combine and season with additional salt if needed. Serve immediately or chill for up to 1 day. Enjoy!