Cut chicken into thin, long slices about 1-inch wide this shape is ideal for skewering and ensures even cooking.
In a large bowl, combine soy sauce, banana ketchup, brown sugar, vinegar, calamansi juice, garlic, pepper, and paprika. Stir until the sugar fully dissolves.
Add chicken slices to the marinade and toss to coat evenly. Cover and refrigerate for at least 4 hours, or overnight for the deepest flavor.
If using bamboo skewers, soak them in water for at least 30 minutes before grilling to prevent burning.
Thread marinated chicken onto skewers, folding each strip accordion-style for the traditional Filipino presentation.
Preheat grill or griddle to medium-high heat. Cook skewers for 3–4 minutes per side, basting with reserved marinade or extra banana ketchup while grilling.
Grill until chicken is fully cooked through with a gorgeous caramelized char on the outside.
Serve hot with garlic fried rice and a chili vinegar dipping sauce on the side.