Gather all the ingredients.
Soak wooden skewers in water for at least 10 minutes.
Finely dice garlic and set aside.
Combine soy sauce, Japanese sake, water, sweetener, bonito flakes, and diced garlic in a sauce pan. Bring it to a boil, then reduce the heat to simmer. Let the sauce simmer for 5 minutes until it slightly reduces. Strain the sauce through a strainer, making sure to press out any extra sauce from the bonito flakes. Split the tare into 2 bowl, one for basting and other for dipping. Note – no need to strain if using hondashi.
While waiting for the sauce to reduce, finely chop green onions and set aside.
In a large mixing bowl, combine ground chicken, toasted sesame oil, remaining diced garlic, miso, chopped green onions, salt, Japanese sake, panko and mix well.
Take about 2 tbsp of chicken/tsukune meatball mix, throw the mix from one hand to another while using the palm of your hands to form a ball about the size of a ping pong ball. Take the meatball and place onto skewer. Take note the meatball mix is very fragile prior to being cooked, so handle with care. Each skewer should hold about 4-5 meatballs. Set on holding plate.
Preheat grill to 350F. Once grill is preheated, reduce heat to medium-low and place skewers on the grill. Using a basting brush, generously brush marinade on each skewer from bowl with 3/4 the sauce and close lid. Rotate skewers every 2 minutes basting on each rotation keeping covered until done, should take around 12-15 minutes or once internal temp reaches 165F. Mix sauce from reserve bowl and drizzle before serving along with sprinkle of optional toasted sesame seed.