Uni shoyu zuke

Combine koikuchi soy sauce, mirin, and sake in a small saucepan. Add kombu.

Gently heat the mixture over low heat until it just begins to simmer, then immediately remove from heat. This process evaporates the alcohol from the sake and mirin and extracts subtle umami from the kombu. Do not boil vigorously.

Remove the kombu from the marinade. Allow the marinade to cool completely to room temperature, then chill in the refrigerator until cold.