Marinade: Whisk soy sauce, brown sugar, sesame oil, olive oil, ginger, garlic, and rice vinegar. Reserve a clean portion for basting if desired (do not reuse raw-chicken marinade).
Marinate: Toss cubed chicken in marinade. Cover and refrigerate at least 1 hour (up to a few hours). Soak wooden skewers in water if using.
Skewer: Thread chicken, pineapple, and red onion alternately onto skewers.
Grill: Preheat grill to medium / about 400°F (200°C). Oil grates. Grill skewers, turning and basting with reserved clean marinade, until chicken reaches 165°F (74°C) in the center, about 8-12 minutes total. Rest briefly and serve.