In a bowl, crack the eggs and mix them. Add sake, salt, and chopped green onion to create the egg mixture.

Heat a tamagoyaki pan over medium heat and lightly coat it with salad oil using a paper towel. Pour 1/3 of the egg mixture into the pan, spread it evenly, and lightly stir. When semi-cooked, place the sweetfish simmered in the center and fold the egg forward.

Push the folded egg to the back of the pan. Reapply a thin layer of oil using a paper towel. Pour another 1/3 of the egg mixture, lifting the folded egg to allow the mixture underneath. Stir lightly and fold forward again when semi-cooked. Repeat the process one more time.