Fill a large bowl with water and add 1 tbsp coarse sea salt (put less if you are using small crystals).
Remove the outer layer of the daikon using a vegetable peeler. Continue peeling long narrow ribbons (lengthwise) until all the daikon is used.
Pare watermelon rind and remove all pink portions. Cut rind in long 1/2 inch thick pieces. Repeat the same step you did for the daikon and use vegetable peeler to make noodles.
Put daikon and watermelon rind noodles in salted water and soak for 15 minutes.
Drain and squeeze the noodles with your fingers to remove excess water. Wrap daikon and watermelon in paper towel and pat dry, to remove as much water as you can without breaking the noodles. Transfer to a bowl and set aside.
Add mayonnaise, sriracha and ginger to the bowl and stir until all the ingredient make a creamy sauce. Season with salt and pepper and serve immediately.