Julienne the daikon radish into matchsticks, about 1/8 inch thick.
In a small saucepan, heat the vinegar and water over medium heat until it begins to simmer. Stir in the xylitol until it is fully dissolved.
Place the sliced radishes and optional bird’s eye chili into a clean glass jar. Pour the hot vinegar mixture over the radish slices, ensuring they are fully submerged. Press the radishes down if needed to make sure they are covered by the brine.
Allow the jar to cool to room temperature before sealing it with a lid, which will take 45 minutes to an hour. Then refrigerate the jar.
The radishes will be ready to eat after a few hours, but their flavor will develop further if left for 24 hours. Leave it in the refrigerator for at least 2 hours, if not more.
Once they are ready, use these pickled radishes as a crunchy, tangy topping for salads, tacos, sandwiches and more!