Mix together the chicken stock, sugar, soy sauce, and cooking wine. Set aside.
In another bowl, beat the eggs. Set aside.
Add the oil to the pan over medium heat. Stir fry the sliced onion in the pan until they are translucent and caramelized.
Pour the stock over the onions and bring the mixture to a boil.
Place the sliced tonkatsu (as many as can fit in the pan) into the mixture, on top of the onions. Drizzle the egg mixture all over everything. Cook over medium high heat until the egg is set to your liking. If you like runny eggs, this could be as little as 1 minute and up to 5 minutes for set eggs.