Remove any pinbones you may find in the cod, and cut each fillet into 3-4 pieces (depending on the size of the fillet). Season with salt and sake, and set aside for 10-15 minutes.Peel the daikon, cut in half lengthwise and grate with a daikon grater. Let it sit in a strainer to drain away the liquid while you prepare the rest of the dish.
Pat the cod pieces dry and coat with flour. Heat a pan to medium-high and add the oil.
Put the cod pieces in the pan skin-side down, and fry til each side is golden in colour, about 2-3 minutes per side.
Put the simmering liquid ingredients in a saucepan and bring to the boil. Mix in the grated daikon and add the cod. Return to a boil, then remove from heat. Serve with the liquid in a shallow bowl.