Soak the bamboo skewers in a bowl of water for at least 30 minutes to prevent burning.

In a medium saucepan over medium heat, combine soy sauce, mirin, sake, and sugar. Stir for 5-6 minutes until the sugar dissolves and the mixture thickens slightly.

Cut the chicken thighs into bite-sized chunks and thread them onto the soaked skewers.

Preheat the grill to medium-high heat and oil the grates with a paper towel dipped in cooking oil.

Grill skewered chicken for about 3-4 minutes on one side. Brush with yakitori glaze and flip, cooking for another 3-4 minutes or until fully cooked.

Serve hot over steamed rice, optionally garnished with sesame seeds or chopped green onions.