01 - Combine soy sauce, mirin, sake, brown sugar, and honey in a small saucepan. Simmer gently over medium heat for 5 to 7 minutes, stirring until the sauce thickens slightly. Cool before use.
02 - In a large mixing bowl, combine ground chicken, chopped green onions, garlic, grated ginger, panko breadcrumbs, egg, soy sauce, sake, sesame oil, salt, and black pepper. Gently mix until just incorporated; avoid overworking the mixture.
03 - With lightly moistened hands, form the mixture into 20 to 24 small meatballs, each about 1.5 tablespoons in size.
04 - Slide 3 or 4 meatballs onto each skewer, pressing gently to secure them along the length.
05 - Heat grill or grill pan to medium-high. Lightly oil the grates to prevent sticking.
06 - Place skewers on the grill and cook for 3 to 4 minutes on each side, turning to ensure even browning.
07 - Brush each skewer generously with yakitori sauce, then grill 1 to 2 minutes longer, turning and brushing with more sauce until the meatballs are glazed and thoroughly cooked.
08 - Transfer hot skewers to a serving platter and garnish with sliced green onions and toasted sesame seeds if desired.