One part soy sauce, one part mirin, one part rice vinegar: this is the ratio for my family's basic oil-free Japanese-style dressing. Feel free to change it up a bit! There are so many different ways to enjoy this!
I'm constantly thinking of various delicious Japanese style oil-free dressings.
You probably have all these ingredients on hand already, so it's easy. Not only is this great as a salad dressing, you can use it with chilled udon noodles, chilled tofu, etc. It's oil-free, but you can add sesame oil or your choice of oil if you want! It also tastes good if you add yuzu or lemon juice! In that case, decrease the amount of vinegar.