Peel the radish and slice them freely (from the side to center as you pivoting the radish to create irregular shape, about 1/2" thick on the top. (see the tutorial)
In a large shallow bowl, dissolve salt in Sprite. Add the radish slices and soak for 1 hour. Toss radishes a couple of times during to get evenly salted.
To make anchovy stock, combine anchovies and sea kelp with about 1 cup water in a pot and bring to boil, simmer for 5 minutes. Remove from heat and let it rest until ready to use.
In a blender, combine garlic, ginger, onion, mashed potato, and pour 1/2 cup of anchovy stock; puree until smooth.
When the radishes are done with soaking, rinse them once. Drain well.
In a small mixing bowl, combine chili flakes, salted shrimp, anchovy sauce, sugar, and the onion garlic puree. Mix well to form thin batter.
In a large shallow mixing bowl, combine radishes and the chili filling. Toss them well to coat the kimchi filling to radish.
Transfer the radish kimchi into an airtight container. Pour 1/2 cup of water to the mixing bowl you used making kimchi. Rinse out all the remaining chili filling residue inside the bowl and pour it over the radish Kimchi.
Cover and let it sit in the room temperature for 1-2 days until you see some tiny bubbles appear on the top surface. You will also see more water is coming out of radishes. Toss well to even out the juice. Store the kimchi in the refrigerator for 1 week and your radish kimchi is ready to serve!