In a small bowl, combine kochu karu, sugar and salt. Rub chile mixture all over pork belly, especially on the top fat. Place in fridge, uncovered, overnight. Pre-heat oven to 350 degrees. Remove pork belly from fridge and score fat on top in a diamond pattern. Pour rice vinegar into roasting pan with flat rack. Place pork belly on rack and cover tightly with foil. Bake in oven for until all the liquid is gone, about 45 minutes to an hour. Let belly rest and come to room temperature. Meanwhile, prepare a hot, clean grill, sprayed slick. Grill pork belly (you can cut it into 2 equal pieces if that's easier for you) until well colored and heated through, about 6 minutes per side. Let pork belly rest for a few minutes. Grill potato buns just until marked. To make the sandwich, top a bun with about 1/2-inch slices of grilled pork belly, add sliced pickles and Clementine Marmalade, add bun top. Enjoy!