Add enough water to a pot to cover the eggs. Bring the water to a boil over high heat. Carefully lower the 6 eggs into the boiling water using a spoon. Cook over medium-high heat for 6–7 minutes for soft-boiled eggs. Immediately remove the eggs from the water once the time is up.

Place the boiled eggs into an ice water bath to stop the cooking process. Once cooled, gently crack the eggshells by tapping them on a flat surface and peel them carefully to avoid damaging the soft whites.

In a clean pot, combine 60g mirin, 60g light soy sauce, 15g white sugar, and 200g water. Stir thoroughly until the sugar dissolves. Heat the mixture until it boils, then turn off the heat and allow it to cool completely.

Submerge the peeled eggs in the cooled marinade, ensuring they are fully covered. Seal the container tightly with plastic wrap or a lid and refrigerate overnight. This allows the eggs to absorb the marinade and develop their signature flavor.