Make the sauce by mixing the soy sauce, mirin and sugar in a sauce pot on the stove. Bring to a boil then turn the heat to medium-low and simmer for about 5 minutes until it is reduced to about a third and slightly thickened. Put to the side.
Put about 5-6 chicken pieces on each skewer.
Using a brush, lightly baste both sides of skewers with sauce and place the skewers on the rack.
Place the baking sheet with rack under the broiler. The distance between the skewers and the broiler should be about 2 inches.
Cook for 5-6 minutes, then take the tray out and turn the skewers over. Baste the cooked side of the skewers with a pastry brush and the sauce and place the tray back under the grill.
Cook for 4-5 minutes, then take the tray out and turn the skewers over again. Baste the chicken and place the tray back under the grill.
Cook for a minute or until the chicken starts getting dark brown in spots. Turn again and baste again to get those dark brown spots.
Remove the skewers off the rack and plate them on a platter. Serve immediately as an appetizer or as a full meal with steamed rice and veggies.