In a large bowl, mix the flour, water, salt, baking powder, and sugar. The batter with be thick. Add the cabbage and mix well until the cabbage is coated. Add the eggs and mix lightly until just combined.
Preheat a cast-iron or a non-stick skillet for 5 minutes on medium heat. Add 1 tablespoon of the sesame oil. Spoon about 1/4 of the batter into the skillet and form a pancake about 6 inches (15cm) in diameter and about 1 inch (2.5cm) thick. Don't press down.
Lay 1/4 of pork slices on top, without overlapping, and cook for about 3 minutes. Flip over so the pork slices are now facing down. Cook for 5 minutes more. Flip again and cook for 2 minutes more or until the cabbage inside is tender and the pork is cooked through. Remove the pancake from pan and place on a plate. Repeat the process with remaining batter.
Now make the Tonkatsu sauce. Combine the ketchup, Worcestershire and oyster sauces, and sugar in a small bowl and whisk together.
Squeeze the Tonkatsu sauce onto the pancake, in long ribbons. Squeeze the mayo onto the pancake, also in long ribbons. To squeeze the homemade sauce use a piping bag or cut a tip off a ziploc bag. Top with some pickled ginger. If you have Aonori or Katsuobushi, use 1 tablespoon of each per pancake. Enjoy!