I'm thinking that it's probably an herb or a spice. I've never used it before, but I came across a recipe that calls for it. Can someone tell me, please? I guess that I can do without it if I can't find it.
There are two kinds of mirin here in Japan, 'Hon Mirin' (true mirin) and what you might call 'regular mirin'. The former is made with real alcohol and has to be purchased at a liquor store, so the second is what most housewives use (and probably what most recipes you'll find use).
The alcohol in the mirin (and sake when called for in recipes) is said to neutralize off smells while adding a touch of sweetness, so it's used with meats a lot. It's likely that your recipe is in balance with soy sauce and sake as well. Different ratios are used for different sauces.
Over here, a white wine can be a quick sub or a dry white wine with a bit of sugar, or so says my neighbor. 😁