Katsuo no tataki ponzu

Prepare the ponzu sauce: Combine koikuchi soy sauce, rice vinegar, yuzu juice, and mirin in a small saucepan. Add kombu and katsuobushi. Gently heat the mixture until just before it boils, then remove from heat and let it steep for 15 minutes. Strain the ponzu sauce through a fine-mesh sieve and allow it to cool completely.

Prepare the garnishes: Peel and finely grate the daikon. Peel the ginger; finely julienne a portion and thinly slice the remaining ginger. Thinly slice the scallions. Thinly slice the garlic. Arrange the shiso leaves on a serving platter.

Sear the katsuo: Pat the katsuo fillet very dry with paper towels. Heat the vegetable oil in a heavy-bottomed pan or cast iron skillet over high heat until it begins to smoke. Carefully place the katsuo fillet in the hot pan and sear each long side for 30-45 seconds until deeply browned but the center remains raw. Also sear the two short ends.