Sub for Sake in teriyaki

i’m considering trying Morimoto’s teriyaki tonight but have no Sake in the house nor opportunity to get any. Any suggestions for substituting? Maybe just more Mirin and less sugar?

When I did not have sake (or did not want to use a high quality sake that I did have), I added rice vinegar.
It was not a 1 for 1 substitution but just enough to add acidity to the mirin/sugar mix.
In other words, I would not use 1/2 cup of vinegar as a substitute for 1/2 cup of sake in Morimoto’s recipe. I would not even use 1/4 cup. I would try a tablespoon and go up from there as required.

For different teriyaki glazes, I occasionally soak dried porcini mushrooms and then add the broth.

yes. for a twist, try a low hopped beer, even a dark one.