Sliced onion with soy rice vinegar dressing
Slice onion very thinly. Use slicer if you have it. Put sliced onion in water with salt (about 1/4 tsp) and leave for 10 minutes or so. Squeeze and dry with a paper towel.
Whisk soy sauce, vinegar, oil and sugar very well in a bowl. Add sliced onion and mix.
Sprinkle with Katsuobushi if you like.