1Combine koikuchi soy sauce, rice vinegar, yuzu juice, mirin, kombu, and katsuobushi in a small container. Let it infuse for at least 30 minutes, or ideally several hours in the refrigerator, to create the ponzu.
3In a bowl, sprinkle Salt over the shirako and gently massage for about 1 minute. Rinse thoroughly under cold water. Transfer the shirako to a separate bowl and pour Sake over it, letting it sit for 5 minutes.