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. Cook for 8-10 minutes until the sauce slightly thickens. 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.
04 - Place skewers on the hot grill. Cook for 3 minutes on each side, brushing generously with the prepared yakitori sauce after each turn. Continue grilling and basting for an additional 6-8 minutes until the chicken is fully cooked and develops a glossy, caramelized coating.
05 - Remove skewers from heat and serve immediately. Drizzle with additional warm yakitori sauce if desired. Best enjoyed hot from the grill.