Prepare the Tare Sauce
Combine soy sauce, mirin, sugar, and sake in a saucepan.
Simmer on low heat for 5-7 minutes until slightly thickened. Remove from heat and set aside.
Make the Chicken Mixture
In a large mixing bowl, combine ground chicken, egg, panko breadcrumbs, soy sauce, sake, sugar, green onion, ginger, salt, and pepper.
Mix thoroughly until sticky and well combined.
Divide the mixture into equal portions and shape them into small oblong patties or balls.
Skewer the Tsukune
Thread the shaped chicken patties onto the prepared skewers.
Grill the Tsukune
Preheat your grill or grill pan over medium heat and brush with vegetable oil.
Place the skewers on the grill and cook for 3-4 minutes per side until golden brown.
Baste with tare sauce and cook for another 2-3 minutes on each side until caramelized and glossy.