Whisk together the pineapple juice, soy sauce, brown sugar, garlic, ginger, sesame oil, rice vinegar, sriracha, smoked paprika, and black pepper until the sugar dissolves.
Place the chicken thighs in a large zip-top bag or shallow dish. Pour the marinade over the chicken, coat evenly, cover, and refrigerate for 4 hours or overnight.
Preheat the grill to medium-high heat (about 400°F). Lightly oil the grill grates to prevent sticking.
Remove the chicken from the marinade and discard the used marinade (or boil it separately if using for basting). Grill the chicken for 5–6 minutes per side.
During the last few minutes of grilling, brush the chicken with the reserved boiled marinade for extra flavor and caramelization.
Continue cooking until the chicken reaches an internal temperature of 165°F (74°C).
Transfer the chicken to a serving platter and let it rest for 5–10 minutes before slicing.
Garnish with sliced green onions and toasted sesame seeds. Serve hot with steamed rice, Hawaiian macaroni salad, or grilled pineapple.