In a large mixing bowl, combine soy sauce, banana ketchup, brown sugar, white vinegar, minced garlic, chopped onion, ground black pepper, salt, and paprika. Stir vigorously until the brown sugar dissolves completely.

Add the chicken thighs to the marinade, ensuring each piece is thoroughly coated. Cover the bowl with plastic wrap or transfer the mixture into a zip-top bag and refrigerate for at least 2 hours, ideally overnight.

Preheat your grill to medium-high heat, around 400°F (200°C). Lightly oil the grill grates to prevent sticking.

Retrieve the chicken from the refrigerator and thread the pieces onto soaked bamboo skewers, leaving about half an inch of space between each piece.

Place the skewered chicken on the preheated grill. Cook for 5-7 minutes on each side, basting with the remaining marinade.

Once cooked, remove the skewers from the grill and let the chicken rest for a few minutes before serving.