Heat oil in a skillet. Sear all sides of the pork belly, starting with the fat side first. This should take about 10 minutes.
Add the remaining ingredients to a large pot. Braise pork belly over low heat for 1 hour. Let cool completely. Chill overnight in braising liquid.
Cut pork belly into thin slices. Brown slides in a frying pan before serving.
For the Broth...
Stir together the broth ingredients and bring to a gentle simmer.
For the Clams...
Bring sake, mirin, and water to a boil in a small pot. Add clams and cover. Cook for about 5 minutes or until clams open.
For the Ramen...
Cook noodles per the instructions on the package. Divide noodles and broth between bowls. Service with 1-2 slices of pork, 4-6 clams, and a 1/2 of an. Garnish with corn and green onions.