Is there any technique that can remove the bitter taste of a daikon radish?
Well, boiling them helps to remove the bitter taste. But that's not what you want to hear, is it? You want fresh grated daikon for your salad, don't you?
First of all, the enzyme that causes the pungency is mostly in the skin, so peeling any radish is a big step away from bitterness. Second, we heard someone bragging once that certain Japanese graters are sharper than normal graters. The sharper blade does not destroy the fiber of the radish, so that the "bitter tang" remains trapped in the fiber cells. It makes sense to us that a sharper blade would rupture fewer cells than a dull grater (or knife), although there are certainly sharp graters available from many countries.
Of course, you don't want to waste a lot of daikon, but the top end just below the leaves is the sweetest part of the radish. After peeling, you might use that for grating and find a cooked use for the rest of the daikon.
Finally, it is a radish, after all, and radishes are generally bitter. People pay serious money these days for the pleasure of eating bitter foods. What's up with you?