Combine the rice vinegar, warm water, sugar, salt, garlic cloves, red pepper flakes, and black peppercorns in a large airtight container. Add the carrots and daikon radish into the container. If the carrots and daikon are not covered, add additional rice vinegar. Cover and place in the refrigerator for at least 4 hours. The longer they are left to pickle, the more flavorful the carrots and daikon will become. Can be stored in the refrigerator for about 2 weeks.