Add the apple, ginger, garlic, green onion, soy sauce, mirin, sesame oil, rice vinegar, sugar, black pepper, and 1 tablespoon of sesame seeds to your blender or food processor. Blend on high for 30-45 seconds until you have a smooth, slightly thick marinade with no large chunks remaining.

Using a sharp knife, cut 2-3 diagonal slits about 1/2 inch deep into each chicken quarter, cutting through the skin and into the meat. Space these cuts evenly across the meatiest parts to help the marinade penetrate and ensure even cooking.

Place chicken quarters in a large zip-top bag or shallow baking dish. Pour the marinade over the chicken, making sure every piece is thoroughly coated and working the marinade into the slits. Seal the bag or cover the dish with plastic wrap, then refrigerate for at least 2 hours or up to 24 hours. If marinating 2-4 hours, flip after 1 hour. For overnight marinating, flip after 4-6 hours.

When ready to cook, preheat your air fryer to 375°F for about 3-5 minutes. Remove chicken from the marinade and shake off excess marinade. You want some coating but not dripping wet. Pat lightly with paper towels if needed.

Arrange chicken quarters in the air fryer basket in a single layer with space between each piece. Most air fryers fit 3-4 quarters. If cooking in batches, keep first batch warm in 200°F oven. Cook for 25-30 minutes, flipping halfway through at 12-15 minutes. Chicken is done when internal temperature reaches 165°F and skin is deeply caramelized with mahogany color and charred edges.

Let the chicken rest for 5 minutes after cooking to allow juices to redistribute. Garnish with remaining toasted sesame seeds and extra chopped green onions before serving.