Gather all the ingredients, noting that 1½ cups (2 rice cooker cups, 300 g) of uncooked rice yields 4⅓ cups (660 g) of cooked rice for 2 donburi servings.

Add 1 cup water and 1 dashi packet to a small pot and cook over medium heat.

Once boiling, reduce to medium-low and simmer for 2 minutes, then discard the packet.

Thinly slice the onion and set aside the sliced green onion for garnish.

Crack 3 large eggs into a bowl and gently lift the whites to create marbled yolks.

Cut the tonkatsu into slices about 1 inch thick.

In a large frying pan, layer the onion and add the dashi.

Cover and cook until the onion is tender.

Add 2 teaspoon sugar and 2 tablespoon mirin, followed by 2 tablespoon soy sauce.

Place the tonkatsu on top and cover until heated through.

Distribute the egg in a spiral over the tonkatsu and cover until just set.

Divide cooked rice into bowls, topping with the mixture of tonkatsu, onions, and eggs. Garnish with green onion.