Sprinkle the fillets with salt on both sides and let it sit aside for 30 minutes. Meanwhile mix miso, sake, grated ginger and sugar in mixing bowl. Pat dry the fillets and slice them into desire size; I prefer 2 inch pieces. Place fillets into Ziplocs bag and pour in marinate; keep refrigerated for 24-36 hours.
Cooking: Prepare broiler. Remove fish from Ziplocs and scrape off excess miso marinate from fish; the miso marinate will burn in the cooking process. Place fillets skin side up on parchment paper and put in broiler. Remove the fish from the boiler once it turns opaque and it is ready to be served with the grated daikon radish!