Simmer the soy beans in salted water until tender, 1 hour 30 minutes to 2 hours. Drain, rinse and cool.
For the dashi broth: Combine the shrimp shells, celery, carrots, parsnips and onions in a large pot. Pour in 12 cups cold water. Bring up to a light simmer, skimming any foam or particles that rise to the surface. Simmer for about 1 hour 30 minutes. Feel free to add any parsley stems or other vegetables you have as long as their flavors are conducive with the dish.
Remove the shrimp shells. Add the seaweed and simmer for 30 minutes. Strain the liquid, return to the pot with the bonito flakes and bring back up to a simmer for 30 more minutes. Strain again and season with salt, lemon and hot sauce, if desired.
For the fish and assembly: Preheat the oven to 400 degrees F. Lightly sprinkle the fish with salt and brush with the sweet soy on both sides. Dredge the fish in the rice flour. Heat the oil mixture in a saute pan until very hot, and then sear the fish until browned on one side. Flip and transfer to the oven to finish cooking for 3 to 5 minutes.
Meanwhile, simmer the soy beans in the dashi broth to warm. Saute the bok choy in a little oil with some salt and the white wine, and then place on the bottom of each of 6 large bowl or dishes, and pile the soy beans in the center. Pour the dashi over the top, just to cover the top of the beans. Place the whitefish on top of the beans, making sure not to submerge in the broth. Top with the grapefruit segments and a small pile of pickled daikon.