Trim the crusts off four slices of shokupan bread and lay them flat on a clean surface.

Hard-boil large eggs using your preferred method and allow to cool for 10 minutes before peeling.

Cut the cooled hard-boiled eggs into quarters and blend with kewpie mayonnaise in a food processor until creamy with some chunks.

Transfer the egg mixture to a bowl, season with salt and pepper, and add scallions if using.

Spread the egg salad filling over two slices of bread, then top with the remaining slices.

Slice each sandwich diagonally and serve on a plate.