My neighbor gave me this simple recipe... knowing I'm not a "rocket scientist" in the kitchen.. and it's pretty good.. as good as the stuff I get in the bottle at the supermarket anyway... you might want to give it a try while you're waiting for a REAL sauce
make 1/2 cup simple syrup (1/4 cup sugar, 1/4 cup water.. heat to dissolve, don't stir)
then add 2 cups soy sauce
add 3 or 4 large cloves of garlic (I put them through my Susi garlic press).. I like garlic and we have a bad vampire problem here in Seattle.
take 1 inch or more fresh ginger ... I grate it on a porcelain grater thing I got at a Chinese shop
You can get fancy and add toasted sesame seeds and onions or whatever.. I don't... yet.
Salt & Pepper... you can adjust everything to your taste of course.. less sugar, less garlic, etc.
Then I toss it all in a small heavy pan... heat it to just starting to boil... simmer for 3 or 4 minutes.. and that's it... I guess if you added some green or other onions and/ or sesame seeds, you'd strain it, then store it.
That makes more of a Chinese teriyaki sauce.. as I understand it, the Japanese version omits the sugar, garlic, & ginger and uses a sweet Japanese wine mixed with the soy.. I forget the name of it now..
I'm sure others have more "sophisticated" recipes.. but this is a start anyway.