Finely grate the daikon and drain it well using a tea towel to remove the liquid. Meanwhile, reduce the mirin, rice vinegar and saké mixture in a saucepan until it thickens. Once reduced, leave it to cool then mix with the daikon.
Using two teaspoons, form the shape of a nigiri with the seasoned grated daikon and put it on a plate. Place one anchovy on top then serve.