Pat the yellowtail fillets dry with paper towels. Mix the marinade ingredients (sake, mirin, soy sauce, water) in a tray, add the yellowtail, cover with thick paper towels and plastic wrap, and refrigerate for 1 hour.

Grate the daikon and drain excess water.

Heat salad oil in a frying pan over medium heat. Remove excess marinade from the fillets and cook each side for 2 minutes until browned and cooked through. Push the fillets to the side, remove excess oil with paper towels, and add the marinade. Spoon the marinade over the fillets and simmer until glossy.