Drain the oil from the canned tuna using a sieve. Keep the oil aside.

In a pot, combine anchovy stock, soy sauce, mirin, and sugar. Bring to a boil to make the sauce.

Heat the tuna oil in a pan.

Add the sliced onion to the pan and sauté until partially cooked.

Pour 350ml of the prepared sauce into the pan with the onions and simmer.

Once the onions are fully cooked, add the drained tuna to the pan.

Add half of the eggs to the pan and cook until partially set. Then add the remaining eggs and cook until fully set.