In a large bowl, combine soy sauce, banana ketchup, brown sugar, white vinegar, minced garlic, chopped onion, ground black pepper, salt, paprika, and water. Whisk together until the sugar fully dissolves.

Cut boneless chicken thighs into bite-sized pieces, then add them to the marinade. Toss to coat thoroughly and refrigerate for at least 2 hours.

Preheat your grill to medium-high heat, about 400°F (200°C). Soak bamboo skewers in water for 20 minutes.

Take marinated chicken pieces from the fridge and thread them onto the soaked skewers, leaving space between each piece.

Cook skewers on the grill for 5-7 minutes per side, basting with leftover marinade until chicken juices run clear.

Remove skewers from the grill and let them rest for a few minutes before serving.