First tenderize pork loin with the back of a knife or meat tenderizer on both sides until it's 1 cm thick. Season both sides with salt.
Place potato starch in a large shallow bowl. Then crack and beat 1 egg in a second large bowl. In the last bowl, spread out panko breadcrumbs. Then evenly dredge the slice of pork into potato starch, then into the beaten eggs and lastly, into the panko breadcrumbs. Make sure there are no bald spots.
Choose ONE cooking method below: Deep Frying Method: Heat 1 cup or 250 ml of vegetable oil in a large pan on medium heat until 350 F with a digital instant read thermometer. Fry coated pork into the hot oil on both sides for 6-7 minutes in total, until golden crispy brown on each side and an internal temperature of 145 F. Remove fried pork and transfer to a wire rack or paper towel lined plate to remove excess oil. Air Frying Method: Lightly spray the air fryer basket with vegetable oil. Transfer the breaded pork to air fryer basket. Lightly spray vegetable oil over the pork. Air fry on one side for 8-10 minutes at 350 degrees F. Then flip over and spray more oil over top and air fry for another 8-10 minutes until golden brown with an internal temperature of 145 F with a digital instant read thermometer. Transfer fried pork to cutting board and slice into ¾-inch wide pieces. Set aside.
Place hot cooked rice in a large 6-8 inch serving bowl. Cover and set aside.
Then in a small saucepan (about 6-8 inches), add water and dried kelp. Bring to medium heat and allow the kelp to simmer for 5 minutes. Remove the kelp and discard. Skim off the bubbles in the water.
Next add bonito flakes to the water. Simmer for 3 minutes over low heat.
Prepare a fine sieve lined with paper towel set over a large bowl and strain the hot broth to remove the bonito flakes. Discard the bonito flakes and pour the liquid back into a clean saucepan. This is your dashi broth.
To the dashi broth, add regular soy sauce, sugar, mirin and onions. Bring to a simmer over low heat and cook until onions are translucent and softened.
Add sliced pork katsu into the center of the pan laying flat over the onions.
Next pour two beaten eggs over the onions and pork in a circular motion. Cook the eggs your desired texture: for runny eggs, cook for 1-2 minutes and for fully cooked eggs, cover and cook for another 1-2 minutes.
Loosen the edges around the egg using a spatula before sliding everything in the pan on top of cooked rice. Enjoy hot!