Assemble all ingredients except the eggs and boil for 1 minute to both evaporate the alcohol in the Mirin and Sake as well as to incorporate the sugar.

Wait until thoroughly cooled

Boil or steam eggs for 6.5 minutes and immediately place in a cold water bath. Add a bit of vinegar and salt to boiling water to facilitate removing the soft boiled eggs from their shells

Add the eggs to a bag with the marinade overnight but not longer than 1.5 days

Serve within 4 days and save the marinade so that you can add more eggs another day