Serve this dipping sauce alongside En Japanese Brasserie's Shabu Shabu.
Place sake and mirin in a small saucepan; bring to a boil. Let boil for 30 seconds. Transfer to an airtight container along with yuzu juice, katsuobushi, soy sauce, and kombu. Cover and refrigerate for 3 weeks.
Strain through a fine mesh sieve; discard solids. Return mixture to an airtight container and add cherry leaves. Cover and refrigerate for 1 week before using.