Prepare chicken thighs by deboning and flattening them out while leaving the skin on.
In a mixing bowl, combine soy sauce, sugar, mirin, sake, minced garlic, and grated ginger.
Pour half of the sauce over the chicken to use as a marinade, and let the chicken marinate for at least thirty minutes up to overnight.
Pour the remaining sauce into a saucepan and heat over medium. Let the sauce reduce slightly. If you prefer a thicker sauce, add your cornstarch slurry.
Grill marinated chicken on high heat until the internal temp hits 165 degrees.
Let rest for five minutes, then slice.
Serve with white rice, iceberg salad, chicken teriyaki, and teriyaki sauce. Garnish with sesame seeds.
