Sake is added to the sauce for umami and flavor. You can use Chicken stock or water+MSG as a substitute for the umami, but there is no suitable substitute for the flavor. If you're concerned about the alcohol, it burns off when you cook it. You can watch this to learn more about why sake is so important in Japanese food: https://youtu.be/C2p6MN4EVeA

I'm glad to hear you were able to find a substitute! Rice syrup will definitely give it a nicer sheen than maple syrup (though it does lose out on the flavor).

In reply to Marc Matsumoto.

P.S. I didn't have maple syrup handy, but found rice syrup worked just great. Thanks again!

I'm so happy to hear this was helpful DJ! Let me know if you run into any problems or have any other questions. I'm always here to help.

As usual, Marc, just perfect, simple proportions for everything. Very similar to my first memorable Japanese cuisine inspiration from NHK in the early 1990s with--you guessed it-- miso chicken. Let me say, I never mastered that recipe--nor any variation--until today. So thanks for resolving several flavor and cooking challenges simultaneously.