Cut fillets into 3 pieces, and blanch in boiling water for a couple of seconds . Remove from water and set aside.

Cut Daikon radish into 1" thick rounds. Then peel and cut into halves. Round off the sharp edges. In a pot boil enough water to cover, and cook Daikon for 15 minutes until easily pierced with a toothpick. Strain water and set aside.

Cut ginger thinly, like matchsticks.

In a medium pot, add water, Soy Sauce, Sake, Mirin, and sugar, and let boil. Add fish, Daikon, and ginger. Cover with parchment paper and cook 25 minutes. Cool completely. Serve at room temperature or reheat.