01 - Combine soy sauce, mirin, sake, sugar, garlic, and ginger in a small saucepan. Bring to a boil over medium heat, then reduce heat and simmer for 8–10 minutes until the sauce coats the back of a spoon. Remove from heat and strain out garlic and ginger pieces.
02 - Thread chicken cubes and spring onion pieces onto soaked bamboo skewers, alternating between meat and onion. Pack pieces closely without overcrowding to ensure even cooking.
03 - Heat grill or grill pan to medium-high temperature. Lightly oil the grates to prevent sticking and ensure easy turning during cooking.
04 - Place skewers on the hot grill and cook for 3 minutes per side. After each turn, brush generously with the prepared yakitori sauce. Continue grilling, turning and basting frequently, for 6–8 additional minutes until chicken is fully cooked and develops a glossy, caramelized coating.
05 - Transfer skewers to a serving platter and drizzle with any remaining yakitori sauce. Enjoy hot while the glaze is still tacky and flavorful.