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 fully dissolves. Reduce heat and simmer for 5 to 7 minutes until the sauce slightly thickens. Remove from heat and let cool.
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 until hot.
04 - Arrange the skewers on the hot grill. Cook for 3 to 4 minutes per side, brushing generously with tare sauce as they cook, until the chicken is cooked through and develops a glossy, caramelized glaze.
05 - Transfer to a serving platter and serve immediately while hot. Offer extra tare sauce on the side for dipping if desired.