In a small bowl, mix together the smoked paprika, garlic powder, onion powder, cayenne pepper, oregano, thyme, salt, black pepper, and brown sugar to create the cajun spice blend.
Pat the chicken thighs completely dry with paper towels, especially the skin side. Drizzle the olive oil over all sides of the chicken, then sprinkle the cajun seasoning generously over every surface, pressing it gently into the skin so it sticks.
For the best results, let the seasoned chicken sit uncovered in the refrigerator for 30 minutes to 1 hour. This helps dry out the skin for extra crispiness. If you are in a rush, you can skip this step.
Preheat the air fryer to 380 degrees F for 3 minutes. Place the chicken thighs skin-side down in the basket in a single layer without overcrowding.
Air fry for 10 minutes, then flip the thighs skin-side up. Cook for an additional 10 to 12 minutes until the skin is deeply golden and crispy and the internal temperature reads 175 degrees F.
Brush the hot chicken with the melted butter as soon as it comes out of the air fryer. This adds richness and helps the spice crust look beautifully glossy.
Let the chicken rest for 3 to 4 minutes, then garnish with fresh parsley. Serve alongside coleslaw, cornbread, or dirty rice for a full cajun-inspired meal.