Start by placing 4 large eggs in a saucepan and cover them with cold water, ensuring the water is about an inch above the eggs. Heat on high and bring it to a rolling boil. Cover, reduce heat to low, and simmer for 10 minutes. Transfer to an ice bath for a few minutes to cool.

After cooling, carefully peel the eggs and place them in a mixing bowl. Mash the eggs softly with a fork. Add 2 tablespoons of Japanese mayonnaise, 1 teaspoon of sugar, and 1 teaspoon of salt. Mix thoroughly until well combined.

Take 2 slices of soft white bread and spread an even layer of the egg mixture onto one slice. Place the second slice on top to create a sandwich. Press gently and repeat with remaining ingredients.

Using a sharp knife, cut each sandwich in half diagonally for presentation. Arrange halves on a plate or pack for a delightful lunch.