Make the teriyaki sauce. In a small saucepan, whisk soy sauce, honey, brown sugar (if using), rice vinegar, mirin, sesame oil, garlic, ginger, and sriracha or chili flakes. Bring to a gentle simmer over medium heat, then whisk in the cornstarch slurry. Cook 1–2 minutes until slightly thickened and glossy.
Remove from heat to cool slightly.
Prep the salmon. Pat salmon fillets dry with paper towels. Dry fish browns better and prevents steaming. Brush lightly with neutral oil and season with a small pinch of salt and pepper. (Go easy on salt because the sauce is salty.)
Preheat the air fryer. Set to 390°F (200°C) for 3 minutes.
Preheating helps the glaze set quickly and prevents sticking.
Brush with sauce. Reserve about one-third of the teriyaki sauce for finishing. Brush the remaining sauce over the top and sides of the salmon. If your air fryer basket tends to stick, spray it lightly with oil or line with perforated parchment made for air fryers.
Air fry. Place fillets skin-side down in a single layer, not touching.
Cook 7–10 minutes, depending on thickness (7 minutes for 1-inch fillets; add 1–2 minutes for thicker pieces). Salmon should flake easily and reach an internal temperature of about 125–130°F for medium or 140°F for well-done, depending on your preference.
Glaze and finish. Brush the reserved sauce over the hot salmon. Sprinkle generously with toasted sesame seeds and top with sliced scallions.
A light squeeze of lemon or lime brightens everything.
Serve. Pair with steamed rice, sesame-sautéed greens, cucumber salad, or soba noodles. Spoon any extra sauce from the pan over your sides.