Peel the radish and slice it crosswise into very thin slices.
In a large bowl, place the sliced Daikon radish and sprinkle the salt over it.
Mix it thoroughly and let it stand for 30 minutes to remove the liquid out of the Daikon Radish.
Drain the radish to remove the pungent flavor. You can use your hands to squeeze out the liquids.
Cut up the tomato and try to remove as many seeds as you can. Add to the radish.
Cut up the onion into thin strips and add it to the bowl too.
In a separate bowl, mix the vinegar, sugar, and pepper until the sugar is dissolved.
Pour this mixture onto the radish, onion, and tomato.
Transfer it into a glass jar or recipient and let it sit in the fridge for 1 hour to marinate.