In a large mixing bowl, combine Ka‘ū Orange sauce, soy sauce, brown sugar, orange zest and salt to make the Ka‘ū orange teriyaki sauce. Let it sit for at least 30 minutes before using. Yield is 7 cups. Orange teriyaki sauce keeps for 2 months under refrigeration.
Place the fish fillets into a zip top bag with ¼ cup of Ka‘ū Orange teriyaki sauce. Seal the bag and refrigerate for one day to marinate.
Remove the fish from the marinade and pat dry. Place the flour, egg and panko into separate bowls to create a 3-step breading station. Dip the fish into the flour to coat, then into the egg and finally into the panko, coating well on both sides; set aside.
In a large pan over medium heat, place enough oil to reach 1/4” depth in the pan. Add the fish gently and fry for 2 to 3 minutes per side or until golden brown. Remove from pan and place onto paper towel-lined plate.
Combine the mayonnaise, 3 tbsp. Ka‘ū orange teriyaki sauce in a small bowl and mix well. Garnish the plate with shiso leaves, shredded cabbage and radish sprouts. Serve the sauce over the fried fish or on the side, for katsu with a new twist!