1) In a mixing bowl, combine all ingredients for the seasoned flour.
2) In a separate mixing bowl, combine dry ingredients for the tempura batter. Beat the egg and cold water together in a separate container. Add egg and water mixture to the dry ingredients and mix.
3) In another mixing bowl, combine the furikake and Japanese breadcrumbs. Line up the 3 bowls in the following order: Seasoned flour, tempura batter, furikake coating. Season the fillets in the seasoned flour. Dip it into the tempura batter and then coat it with the Japanese breadcrumbs mixture.
4) Heat a deep pot halfway filled with the oil to 180C. Fry the ahi in the oil until brown, turn and fry for an additional minute.
Drain and serve while hot.