Combine all ingredients in a saucepot and reduce slowly until mixture becomes thick.
Preheat a grill.
Soak bamboo skewers for 1 hour in water. Cut each chicken thigh into 1-inch by 1-inch cubes. Cut negi into 1 1/4-inch length pieces. Alternate three chicken pieces and three negi pieces on each skewer, 1 inch apart.
Place the skewers on the grill and cook on both sides for about 3 to 4 minutes. Then, baste the skewers with the teriyaki sauce and continue to cook for about 2 minutes to 3 minutes while continuing to baste. Once off the grill, baste chicken skewer with teriyaki sauce 1 last time, and serve.