Pat chicken thighs completely dry with paper towels. Mix garlic powder, onion powder, salt, and pepper; rub evenly over the skin and underside of each thigh.

Combine soy sauce, honey, mirin, sesame oil, minced garlic, and grated ginger in a small saucepan. Simmer over medium heat 3–4 minutes until slightly reduced. Stir in the cornstarch slurry and cook 30 seconds until glossy. Set aside.

Preheat air fryer to 380°F for 3 minutes. Place thighs skin-side up in a single layer. Cook 20 minutes without opening the basket.

Brush thighs generously with teriyaki glaze. Cook 3–5 more minutes until glaze caramelizes to deep amber. Pull at 165°F internal temp minimum — 175°F produces fall-off-bone texture.

Rest 5 minutes. Brush with remaining glaze, garnish with sesame seeds and sliced green onions, and serve immediately.