Peel the daikon radish thickly, and then shave the edges of the slices off. Parboil the daikon radish in the rinsing water from washing rice, or with 1 tablespoon of rice added to plain water.
Parboil for about 20 minutes. When the daikon radish is translucent, drain and rinse. Line the pan with kombu, add fresh water and simmer the daikon radish again.
If you don't have kombu, you can add some mentsuyu to the water and simmer the daikon radish. I didn't have a lot of kombu, so I added both.
Slice the pork belly in to 1 cm thick pieces.
Brown the pork well in a frying pan without adding oil. Wipe away any excess grease or fat that runs out of the meat.
Bring a pan of water to a boil and boil the browned pork to remove more oil (about 5 minutes).
Put the parboiled daikon radish and pork in a deep pot, and add enough water to cover. Then add the sake, mirin, and sugar. Bring to a boil.
When it comes to a boil, turn the heat down to low, add the soy sauce and simmer. I put the pot over a portable stove/heater in the winter to simmer this.
After simmering for about 15 minutes, taste. It's OK if the taste is rather light, but you can adjust by adding mentsuyu if you prefer.
Simmer for as long as you like. You can decide when to stop by looking at the color of the daikon radish. The liquid in the pot should be reduced to about half its original volume.
Bonus: If you cut each 4 cm thick piece of daikon radish into about 6 pieces, it will cook a lot faster. If you do this, reduce the seasoning ingredients to 2 tablespoons each.
Bonus 2: If you don't mind the flavors blending in, use chicken, bacon, fish, atsuage... anything you like.