Make the Marinade. Whisk together soy sauce, ginger, garlic, rice vinegar, onion powder, and brown sugar in a bowl. Reserve ⅓ cup for the glaze.
Marinate the Salmon. Pour the remaining marinade into a shallow dish. Place salmon skin-side up in the marinade. Cover and refrigerate for 15-30 minutes.
Air Fry. Preheat the air fryer to 400°F. Place salmon skin-side down in the basket. Brush lightly with marinade and discard the rest. Cook for 8-10 minutes, depending on thickness.
Thicken the Glaze. While the salmon cooks, bring the reserved marinade to a simmer in a small saucepan. Whisk together 2 tablespoons of water and 1 tablespoon of cornstarch, then stir into the sauce. Simmer until thickened.
Serve. The salmon is done when it reaches 145°F internally and flakes easily with a fork. Spoon warm glaze over the top and garnish with sesame seeds if desired.
