Step 1: Prepare the Tentsuyu Sauce

In a small saucepan, combine the dashi, soy sauce, mirin, and sugar. Bring the mixture to a boil while stirring continuously. Lower the heat to medium and simmer for an additional 2 minutes, ensuring the sugar dissolves completely and the flavors meld harmoniously. Remove from heat and set aside.

Step 2: Prepare the Shrimp

Peel the shrimp, leaving the tails intact for presentation. To devein, use the tip of a wooden skewer or toothpick to carefully lift and remove the dark vein without slicing the shrimp. Make two shallow crosswise cuts along the underside of each shrimp to prevent excessive curling during frying. Rinse the shrimp in cold water, pat them dry, and arrange them on a cutting board.

Step 3: Heat the Oil

Fill a deep, heavy-bottomed skillet or Dutch oven with enough oil to reach about 2 inches in depth. Heat the oil over medium-high heat until it reaches 350°F, monitoring the temperature with a thermometer for consistency.

Step 4: Prepare the Tempura Batter

In a small mixing bowl, whisk together the cold seltzer and egg until frothy. Skim off any foam, if necessary. In a separate bowl, combine the chilled flour with the salt. Gradually add the egg mixture to the flour, gently mixing with chopsticks or a spatula until just combined. Avoid overmixing; the batter should remain slightly lumpy. Keep the batter in the refrigerator until ready to use.

Step 5: Fry the Shrimp

Using a fine mesh sieve, lightly dust the shrimp with cornstarch for better adhesion of the batter. Line a baking sheet with parchment paper and place a wire rack on top. Hold each shrimp by the tail, dip it into the batter, and gently place it into the hot oil. Fry in small batches of about three shrimp at a time to prevent overcrowding. Turn the shrimp once during frying, cooking each side for approximately 1 minute until golden brown. Transfer the cooked shrimp to the wire rack to drain excess oil. Skim any floating debris from the oil between batches to maintain clarity and temperature.

Step 6: Serve

Before serving, gently press and remove excess moisture from the grated daikon radish. Divide the tentsuyu sauce into individual dipping bowls, garnishing each with a small amount of daikon. Serve the shrimp tempura immediately, accompanied by the prepared sauce.