Combine the soy sauce, mirin, sake, sugar, and ginger in a small saucepan.
Simmer for 5 to 7 minutes until slightly thickened. Cool before using.
Skewer and Grill:
Thread the chicken and scallions onto soaked skewers, leaving a little space between pieces.
Brush lightly with oil and grill or broil over medium-high heat for 8 to 10 minutes, turning often.
Brush with tare during the final few turns, cooking until glossy, charred in spots, and cooked through. Season some skewers with salt instead if desired.
Serve:
Arrange the skewers on a platter and serve hot with lemon wedges and extra tare.
Notes
Do not brush on the tare too early or the sugar can burn.
Chicken thighs stay juicier than breast meat on the grill.
Use a broiler rack if grilling outdoors is not practical.