Start by filling a large bowl with ice water and set aside.

In a medium pot, bring water to a rolling boil over medium-high heat. Carefully add the eggs, boiling them for 7-10 minutes.

Transfer the eggs to the prepared ice bath immediately after boiling and let them chill for 2 minutes.

Gently crack and peel the eggs, preferably under running water.

Mash the peeled eggs in a mixing bowl, then add sugar, salt, black pepper, and Japanese mayonnaise, mixing until creamy.

Spread softened butter on one side of each slice of Japanese milk bread. Spoon the egg salad onto one slice and top with another slice.

Trim the crusts and cut the sandwiches in half for serving.