I am running low on mirin -- got any recommendations for substitutions? Would vinegar and sugar work?

I have a question about step 1 on the recipe "Misoyaki Roast Chicken with Shoyu Onion Sauce" from timWuNotWoo. It says:

"Mix the mirin into the miso paste to loosen it up until you get something like the consistency of a gravy or a fresh banana smoothie. Some miso pastes are thicker than others, so if it’s too thick, just add more mirin. Easy beans."