To make the crab filling, mix the crab, imitation crab, onion and ¼ cup mayonnaise together in a bowl and season with 1 tsp. salt, ½ tsp. pepper and ¼ tsp. sugar then set aside.
Cut the Ahi in half. Butterfly each piece in the center about ½ inch thick, trying not to cut all the way through. Cover a sushi mat with a piece of plastic wrap then place a nori sheet on top. Lay the Ahi slice on the edge of the nori and sprinkle with garlic salt and ¼ tsp. pepper. Spread ¼ to ½ cup of the crab mix on top then roll the sushi tightly, wetting the edge of the nori to seal. Refrigerate roll until set, at least 15 minutes, before cooking. Repeat process for second roll.
To make the sauce, combine 1 cup mayonnaise, lemon juice, Beni Shoga, sesame seeds, ½ tsp. salt, ½ tsp. pepper, ½ tsp. sugar, green onions and wasabi then set aside.
To make the batter mix the flour, water and ½ tsp. salt together then set aside. Heat a pot of oil on medium-high heat and remove the plastic wrap from the rolls. Then using your fingers or a brush spread a thin layer of the batter over the whole roll, dipping the ends too. Next, roll in panko. Deep fry until golden brown on the outside, about 4 minutes for rare Ahi or 6 minutes for medium. Let cool, then slice and drizzle with sauce.