• In a sauce pan: add sake, mirin, soy sauce, sugar and whisk everything together. Cook on high heat for 3-5 minutes or until the sauce thickens and reduced to about 1 cup. make sure to stir frequently. Let cool at room temperature or place in the refrigerator for 1 hour. It will thicken as it cools. Divide the sauce in half (one is for the marinade & the other is for brushing over the chicken after it's been cooked).
• Trim off fat from the chicken thighs and cut into 2" cubes. Place the chicken in a shallow dish. Add ½ cup (about half) of the teriyaki sauce, ginger, garlic and mix everything together until well coated. Cover and marinate for at least 2 hour or overnight (preferably).
• Soak the 6" skewers in water for 1 hour. Thread the marinade chicken into the skewers. You should have about 7-9 skewers.
• Preheat the air fryer to 400°F for 10 minutes. Then, coat the basket with cooking spray. Place chicken skewers on the basket and brush with marinate sauce, then discard the sauce.
• Cook for 12 -13 minutes total. Flip the skewers after 6 minutes, brush with teriyaki sauce (the other half). The chicken should be fully cooked (internal should be about 165°F).Transfer the skewers to a plate and brush with teriyaki sauce. Tent with aluminum foil until ready to serve. 

Garnish with sesame seeds & chopped green onions. Serve with rice, vegetables or salad. Enjoy!