The cooking liquid used to make the meat balls (water, if you don't have any)
Light brown sugar (or white sugar)
Prepare the chicken meatballs (Recipe ID: 2569745). Once the meatballs are cool, take them out of the cooking liquid and drain.
Strain the cooking liquid to use it to make the yakitori sauce. If you don't have the meatball cooking liquid, you can just use water. Put all of the sauce ingredients into a saucepan and put over heat.
Simmer until the sauce has reduced to about half the original volume, being careful not to let it boil over. It'll thicken as it cools, so stop heating when it's still a bit on the thin side.
As the sauce thickens, the bubbles, which started out small, will become bigger. It'll burn more easily as you near the end, so be careful.
Transfer the finished sauce to a clean container with a lid. It'll keep for a long time in a cool, dark place. You can use it as a teriyaki sauce or for rice bowls.
This sauce will taste better when it's been aged, so you should make and store it when you can.
The sauce will be even more flavorful if you cook it with grilled chicken skin or chicken bones. If you don't have any, you can use them for your next batch!
Use an oven toaster or a fish grill to grill the meatballs. Baste the meatballs with the sauce and then grill again. Repeat this 2-3 times until they are nicely browned.
When you're done grilling, baste with the sauce one last time, and serve on a plate. You can sprinkle on some shichimi spice if you like.
[Related recipe] Fluffy egg soup, using the cooking liquid of chicken meatbalsl Recipe ID: 2564974
[Related recipe] Yakitori made using a frying pan Recipe ID: 2583206
Story Behind this Recipe
If you marinate the meatballs in the sauce, you cannot store the leftover sauce for sanitary reasons. If you are storing the sauce over a long period of time, it would be more sanitary to keep the sauce separately and use only as needed. If you plan on using it up, you can just marinate. The sauce made with the chicken cooking liquid, full of the chicken flavor, is quite exquisite.
There are a lot of sugar in this sauce, which will cause it to boil over and burn more easily if the heat is too high, so be careful. All of the seasonings used in this recipe are of equal amount, so it's easy to make the necessary amount of it. This sauce has less salt and is on the sweet side. You can vary the amount of the seasonings to your taste.