Prepare an ice bath by filling a large mixing bowl with ice water.

Boil enough water in a medium saucepan, then gently lower in the eggs using a slotted spoon. Cook for 7-10 minutes depending on your soft or firm preference.

Transfer the boiled eggs into the ice bath to cool for about 2 minutes.

Peel the cooled eggs and mash them gently in a bowl, then mix in sugar, salt, black pepper, and Japanese mayonnaise until creamy.

Spread softened butter on both slices of Japanese milk bread and scoop the egg salad onto one slice before topping with the other slice.

Slice the sandwich in half and serve immediately or wrap in plastic for storage.