Spread 2 tbsp kiwi over 350 g beef steak surface in a thin, even film. Wrap it or seal it in a bag and refrigerate for 30 minutes to 1 hour, and stop early if the surface turns swollen or slippery. Wagyu can skip this and go straight to salting.
Scrape the kiwi paste off and rinse the beef under cold running water until the kiwi is completely washed away. Blot every side dry until the surface feels only just damp.
Season both sides evenly with ¼ tsp salt (in total) and 1 pinch ground black pepper. Then leave the beef at room temperature, 15 to 20 minutes.
While the beef rests, make the dip. Dissolve ⅛ tsp dashi granules in 3 tbsp hot water. Warm it with 1 tsp mirin and let it bubble briefly, then stir in 1 tbsp Japanese soy sauce (koikuchi shoyu) and take it off the heat. Heat cooking oil for deep frying to 170 °C (338 °F) to 180 °C (356 °F).
While the oil heats, whisk 1 egg white with 1 tbsp cornstarch and 1 pinch salt. Dust the beef all over with 4 tbsp all-purpose flour and tap off the excess.
Dip the beef through the egg white and let the excess drip off, then press it firmly into 100 g panko breadcrumbs, coating every face and side.
Slide the beef into the oil and leave it still for the first minute, then flip it once. Bring the center to 54 °C (129 °F) to 60 °C (140 °F), about 1.5 minutes per side, and lift it out the moment it reaches temperature.
Set the beef on a wire rack and rest it for 4 to 5 minutes.
Cut it against the grain into strips about 1.5 cm wide, letting the knife pass through the panko first in a gentle sawing motion. Fan the slices rosy-side up with a pile of shredded cabbage. Set the dip alongside and dab wasabi paste onto each slice just before eating. Enjoy!
Notes
Do not over-soften the beef with kiwi: The enzyme keeps working the whole time it sits. Stop too soon and it stays tough to chew. Go past an hour and the surface turns to ragged mush that frying cannot fix. Check it on the early side.Let the beef lose its chill before frying: The fry lasts barely a minute or 2, too short to warm a fridge-cold center, and a cold steak lands raw inside. The 15 to 20 minutes at room temperature is what brings the center up to a warm medium-rare.Pull it early and trust the rest: The whole fry is over in about 1 1/2 minute a side, and the real risk is waiting for more color and cooking the pink out. Let 4 to 5 minutes of carryover heat bring the center up the last few degrees.