01 - Combine soy sauce, mirin, sake, sugar, garlic, and ginger in a small saucepan. Bring to a boil over medium heat, then reduce to a simmer for 8–10 minutes until slightly thickened. Remove from heat and discard the garlic and ginger pieces.
02 - Thread chicken cubes and spring onion pieces alternately onto the pre-soaked bamboo skewers, ensuring even distribution for consistent cooking.
03 - Preheat grill or grill pan over medium-high heat. Lightly oil the grates to prevent sticking during cooking.
04 - Place skewers on the grill and cook for 3 minutes on each side, brushing generously with the prepared yakitori sauce after each turn. Continue grilling, turning and basting frequently, for an additional 6–8 minutes until chicken is cooked through and develops a glossy, caramelized coating.
05 - Transfer skewers to a serving platter and drizzle with remaining yakitori sauce if desired. Serve immediately while hot.