Peel and cut the Daikon Radish into sticks or 1/4–1/2" rounds, depending on how you plan to use it; rinse and pat dry.
In a small saucepan, combine about 1 cup of Water with the Dried Gardenia Seeds and bring just to a gentle simmer; simmer 8–10 minutes until the liquid turns a clear yellow, then strain and reserve the colored infusion, discarding the seeds.
In a clean saucepan, combine the gardenia infusion with additional water as needed, then add Rice Vinegar, Granulated Sugar and Kosher Salt; warm gently and stir until the sugar and salt are fully dissolved — do not boil vigorously.
Taste the brine and adjust sweetness or acidity to your preference: it should be noticeably sweet with a bright vinegar tang.
Place the prepared daikon into a clean jar or nonreactive container and pour the warm (not piping hot) brine over it, making sure the pieces are fully submerged.
Let the jar cool to room temperature, then seal and refrigerate. The danmuji will develop flavor after 12–24 hours, but is best after 48–72 hours.
Store the pickled daikon in the refrigerator for up to 2–3 weeks. Use as a crunchy, colorful accompaniment for sandwiches, kimbap, or as a palate-cleansing side.
