Cook the eggs to your preferred soft-boiled doneness (e.g., 6.5 - 7 minutes for jammy yolks). Immediately cool in ice water. Refrigerate the cooked eggs until ready to use.
2
4 tbsp soy sauce
4 tbsp mirin
4 tbsp water
1 tsp sugar
Prepare the marinade: Combine the soy sauce, mirin, water, and sugar. Optional: Mix and bring to a simmer until the sugar is dissolved, then let it cool down completely.
3
Transfer the cooled marinade to a plastic or Ziploc bag. Peel the cooked eggs and add them to the marinade bag. Ensure the eggs are mostly submerged. Seal the bag and let the eggs rest in the fridge for 12–24 hours.
4
The eggs are ready to use. Do not reuse the marinade for a new batch of eggs!