Cut negi into 2 inch lengths and separate the green parts and white parts. For white parts, make an incision lengthwise and remove the soft green core. Keep it with the green part, which will be used later on for cooking.
Stack up the white part of negi and slice thinly. Soak in cold water for 10 minutes and drain well. Put it in an airtight container or cover with plastic wrap. We will use this for garnishing chashu later.
Sprinkle and rub the salt on the pork belly.
Heat the oil in a cast iron skillet (or regular frying pan) over high heat and brown the fat side first, then flip over to brown the other side. It’ll take about 10 minutes.
While browning, put all the ingredients for seasonings in a heavy bottomed pot (or regular pot).
Place the pork belly in the pot and add ginger and negi and bring it to a boil.
Place an otoshibuta (drop lid) on top of the meat. If you don’t have one, make one out of aluminum foil. Do not use a regular lid.
Lower the heat to medium low and simmer, occasionally turning, for about one hour or until there is ¼ inch liquid left in the pot.
Remove the otoshibuta and reduce the sauce until you can see the bottom of the pot when you scrape the sauce. Stay in the kitchen as the meat can easily get burnt if there is no liquid left. After 15 - 20 minutes or so, bubbles start to appear. You are getting close to the end. Turn off the heat when you see the bottom of the pot when you slide the meat around. The sauce is now thickened and meat is shiny.
Take out the meat and cut into thin slices.
Transfer to a serving plate and top with Shiraga Negii. Or serve with ramen.