Make the sauce. In a bowl or a liquid measuring cup, combine 3 Tbsp sake, 3 Tbsp mirin, 2 tsp sugar, and 2 Tbsp soy sauce. Mix well. You can save the sauce for up to a week.
Cut off the core of the cabbage and shred the cabbage into thin slices. I like using this cabbage slicer that yields super fine shredded cabbage.
Cut the negi (green onion/leeks) as much as you like to use. Here I use about 2-3 Tbsp of chopped negi for one serving. Grate the ginger until you have about 1 tsp for one serving.
I'm cooking one serving at a time. Heat a non-stick frying pan on medium-high heat and place the pork belly slices without too much overlapping. It’s okay if it does a little bit. Once the oil starts to release from the pork, add in the sauce. Note: If you’re using a stainless steel frying pan or cast iron skillet, I recommend applying a little bit of oil first. The oil from the pork belly should be enough to cook the meat without sticking to the pan.
Then add the grated ginger and chopped negi.
Mix the ginger and negi in the sauce. Flip the meat once in a while to cook thoroughly.
Place shredded cabbage on a serving plate and transfer the ginger pork belly and sauce. Serve immediately.