This is a refreshing sweet onions dish since it's mixed with umeboshi, vinegar, sugar and mayonnaise. It's easy and delicious.
I've been making this dish for a while now since I love sweet onions and umeboshi. You could also swap the onion for julienned daikon radish.
Rub the onion with salt before soaking it in water. When using sweet onion, do not soak for too long.
Enjoy Japanese food around the world.