Preheat the air fryer to 400°F (200°C) for 5 minutes.
Pat the salmon fillets dry with paper towels.
Brush both sides of the salmon fillets with olive oil.
Season the salmon evenly with salt and black pepper.
Place the salmon fillets skin-side down in the air fryer basket, making sure they do not overlap.
Air fry the salmon for 10 to 12 minutes, or until the salmon flakes easily with a fork and reaches an internal temperature of 145°F (63°C).
While the salmon is cooking, prepare the Kewpie mayo sauce by mixing Kewpie mayonnaise, soy sauce, and lemon juice in a small bowl until smooth.
Once the salmon is cooked, carefully remove it from the air fryer and place on serving plates.
Drizzle the Kewpie mayo sauce evenly over the top of each salmon fillet.
Garnish with chopped fresh chives and serve immediately.