Begin by placing 4 large eggs in a pot and covering them with cold water. Bring the water to a rolling boil over medium-high heat and let the eggs boil for exactly 10 minutes. Once the time is up, carefully transfer the eggs to an ice bath to cool for about 5 minutes.

Once the eggs have cooled, gently tap them on the counter to crack the shells and peel them under running water. Place the peeled eggs in a mixing bowl and mash them with a fork until they reach a chunky yet creamy consistency.

Add 2 tablespoons of Japanese mayonnaise, 1 teaspoon of sugar, and 1 teaspoon of salt to the mashed eggs in the bowl. Use a spatula or a fork to blend these ingredients together until well combined.

While the egg mixture settles, take 4 slices of soft white bread and lay them on a clean surface. Ensure the slices are fresh and free of crust for a softer bite.

Spread the egg filling evenly across two slices of bread. Place the remaining two slices of bread on top to create two complete sandwiches.

Using a sharp knife, cut each sandwich into halves or quarters. Arrange the pieces neatly on a plate and serve.