In a small saucepan, whisk soy sauce, honey, mirin, rice vinegar, garlic, ginger, sesame oil, and water. Bring to a gentle simmer over medium heat.
Stir cornstarch with 1 tablespoon water to make a slurry. Whisk into the simmering sauce and cook 1–2 minutes until glossy and thick enough to coat a spoon. Remove from heat.
Pat chicken dry. Trim excess fat. Cut into 1.5-inch pieces for faster, even cooking (or leave whole thighs if you prefer). Season lightly with salt and pepper.
Toss chicken with 3 tablespoons of the teriyaki sauce and 1 tablespoon oil. Let sit 10–15 minutes while your air fryer preheats. Reserve the rest of the sauce for glazing.
380°F (193°C) for 3–5 minutes. A warm basket gives that caramelized edge you want.
Arrange chicken in a single layer with space between pieces. No pile-ups. Work in batches if needed.
Cook at 380°F for 7 minutes. Shake the basket or flip pieces halfway through.
Brush chicken with more teriyaki sauce. Air fry 3–5 more minutes until internal temp hits 165°F (74°C) and edges look slightly charred and sticky.
Toss cooked chicken with additional warm teriyaki sauce in a bowl to coat every piece. Don't be shy—this is the money shot.
Sprinkle sesame seeds and green onions. Serve over rice, noodles, or steamed veggies. Squeeze a little lime if you like zing.