01 - In a mixing bowl, whisk together soy sauce, mirin, brown sugar, honey, rice vinegar, minced garlic, grated ginger, and sesame oil until the sugar dissolves and the mixture is smooth.
02 - Transfer approximately 1/4 of the marinade into a small saucepan and set aside for later use as a finishing glaze.
03 - Pour the remaining marinade over the chicken pieces and toss to coat evenly. Cover and refrigerate for at least 30 minutes, or up to 2 hours for deeper flavor penetration.
04 - If using wooden skewers, submerge them in water for at least 20 minutes to prevent burning during grilling.
05 - Remove chicken from the marinade, allowing excess to drip off. Thread the pieces onto skewers, leaving a small gap between each piece for even cooking.
06 - Preheat a grill or grill pan over medium-high heat until it reaches proper cooking temperature.
07 - Place skewers on the grill and cook for 12 to 15 minutes, turning occasionally with tongs, until the chicken is cooked through and develops a light char on the edges.
08 - While the skewers grill, bring the reserved marinade in the saucepan to a rolling boil over medium heat. Simmer for 2 to 3 minutes until the sauce thickens to a glossy glaze consistency.
09 - Brush the thickened glaze generously over the grilled skewers. Sprinkle with toasted sesame seeds and sliced spring onions. Serve immediately while hot.