01 - Combine soy sauce, mirin, sake, sugar, garlic, and ginger in a small saucepan. Bring to a gentle boil over medium heat, stirring until the sugar dissolves. Reduce heat and simmer for 5-7 minutes until the sauce slightly thickens. Remove from heat and let cool completely.
02 - Thread chicken and scallion pieces alternately onto the soaked bamboo skewers, distributing evenly.
03 - Brush a grill or griddle pan with vegetable oil and preheat over medium-high heat.
04 - Arrange the skewers on the hot grill. Cook for 3-4 minutes per side, brushing generously with the tare sauce as they cook, until the chicken is cooked through and achieves a glossy, caramelized glaze.
05 - Transfer the yakitori to a serving platter and serve hot with extra tare sauce on the side.