01 - Combine soy sauce, mirin, sake, sugar, garlic, and ginger in a small saucepan. Bring to a boil over medium heat, then simmer for 8–10 minutes until slightly thickened. Remove from heat and discard garlic and ginger.
02 - Thread chicken and spring onion pieces alternately onto soaked bamboo skewers, ensuring even distribution.
03 - Preheat grill or grill pan over medium-high heat. Lightly oil the grates to prevent sticking.
04 - Grill skewers for 3 minutes on each side, brushing with yakitori sauce after each turn. Continue grilling, turning and basting, for another 6–8 minutes until chicken is cooked through and develops a glossy coating.
05 - Serve immediately, drizzled with extra sauce if desired. Best enjoyed hot off the grill.