In a small bowl, combine soy sauce, honey, mirin, rice vinegar, sesame oil, minced garlic, and grated ginger. Stir well to create the teriyaki sauce base.
In a separate small bowl, mix cornstarch and water until smooth to create a slurry.
Pour the cornstarch slurry into the teriyaki sauce base and stir to combine.
Transfer the sauce mixture to a small saucepan and cook over medium heat, stirring constantly until the sauce thickens, about 2-3 minutes. Remove from heat and let cool slightly.
Pat the salmon fillets dry with paper towels. Place them in a shallow dish and pour half of the teriyaki sauce over the salmon, turning to coat evenly. Let marinate for 5 minutes.
Preheat the air fryer to 400°F (200°C) for 3 minutes.
Place the salmon fillets skin-side down in the air fryer basket, making sure they are not touching.
Air fry the salmon at 400°F (200°C) for 10 minutes, or until the salmon is cooked through and flakes easily with a fork.
During the last 2 minutes of cooking, brush the salmon with the remaining teriyaki sauce for a glossy finish.
Remove the salmon from the air fryer and transfer to serving plates.
Garnish with sesame seeds and sliced green onion before serving.