Cut chicken into 2 ½ centimetre pieces and place in a shallow dish.

Add tamari, mirin, sake, sugar, garlic, and ginger to a saucepan and bring to a simmer over medium heat. Cook, uncovered for 10 minutes or until thickened. Reserve 4 tablespoons of sauce for serving. Pour remaining sauce over chicken, cover, and chill for at least 1 hour.

Meanwhile soak wooden skewers in water for 1 hour.

Preheat barbecue or grill pan. Thread chicken onto skewers and grill for 5 minutes per side or until chicken is cooked through.

Serve drizzled with reserved sauce and sprinkled with sesame seeds.