Combine pineapple juice and soy sauce in bowl.
Add brown sugar and whisk until dissolved.
Mix in ketchup, garlic, and ginger.
Add rice vinegar and sesame oil.
Season with black pepper and mix well.
Place chicken thighs in ziplock bags.
Pour marinade over chicken pieces.
Seal bags and refrigerate for hours.
Preheat grill to medium-high heat.
Remove chicken from marinade, reserve liquid.
Grill chicken skin-side down for minutes.
Flip and baste with reserved marinade.
Continue grilling, turning every few minutes.
Cook until internal temperature reaches degrees.
Let chicken rest for minutes before serving.