Trim and cut the Pork Belly into large 2–3 inch (5–7 cm) cubes so they hold together while braising.
Parboil the pork: place the pork cubes in a pot, cover with cold water, bring to a boil and simmer 3–5 minutes to remove impurities; drain, rinse the pieces and clean the pot.
Prepare aromatics by slicing the Ginger into thick slices and chopping the Japanese Long Onion into 2–3 inch pieces; these will flavor the braise.
In a clean pot combine the Dashi with Sake, Soy Sauce, Mirin and Sugar — adjust proportions so the liquid just covers the pork (a typical ratio is about 3 cups dashi, 1/2 cup soy, 1/2 cup mirin, 1/3 cup sake and 1/4–1/3 cup sugar, but tweak to taste).
Add the parboiled pork, sliced Ginger and Japanese Long Onion to the braising liquid, bring to a gentle simmer, then lower the heat to maintain a bare simmer; cover partially and cook slowly for 1.5–2.5 hours until the pork is very tender (or use a pressure cooker for about 25–40 minutes).
About 45–60 minutes before the end of cooking, peel and cut the Daikon into thick rounds and add them to the pot so they can simmer and soak up the braising flavors.
Soft- or hard-boil the Eggs to your liking (soft-boiled about 6–7 minutes), peel them and add to the braise during the last 20–30 minutes so they absorb color and flavor.
Occasionally skim excess fat and foam from the surface; when the pork and daikon are tender, remove them and the eggs and set aside.
Reduce the braising liquid over medium-high heat until slightly thickened and glossy, then return the pork, daikon and eggs to the sauce and warm through so they become well coated.
Serve the Buta Kakuni hot with a little Karashi on the side for a spicy contrast and sprinkle chopped Scallions over the top. Leftovers taste even better the next day as the flavors deepen.
