1Prepare the dashi stock: gently simmer 10g kombu in 500g water for 10 minutes just below boiling, then remove the kombu. Bring the water to a boil, remove from heat, add 10g katsuobushi, let steep for 30 seconds, then strain through a fine-mesh sieve. Set aside 40g of the prepared dashi stock for the ponzu sauce.
2Combine koikuchi soy sauce, rice vinegar, yuzu juice, and the 40g prepared dashi stock in a small bowl to make the yuzu ponzu sauce. Stir well and set aside.