In a bowl, combine soy sauce, calamansi juice, garlic, ½ teaspoon of the salt and ¼ teaspoon of the pepper. Whisk until well combined.
Add chicken and toss to fully coat. Marinate for 4 hours or overnight. Drain chicken from marinade and pat dry.
In a shallow dish, combine flour, corn starch, baking powder, and the remaining ½ teaspoon salt and ¼ teaspoon pepper. Whisk well.
Dredge chicken in flour mixture to fully coat.
In a wide, thick-bottomed pan over medium heat, heat about 2 inches deep of oil to 350 F.
Add chicken in batches and cook, turning on sides, until golden brown, crisp, and cooked through.
Remove from pan and drain on a wire rack. Serve hot.