Step two: Make the marinade
In a bowl, combine the soy sauce, brown sugar, garlic, mirin, ginger, pineapple, onion, Sriracha, and sesame oil. Pour the marinade over the ribs, shaking the dish so the marinade gets all up in there. Cover and refrigerate for at least 4 hours, but 12 to 24 hours is better! Remove the ribs from the fridge 30 minutes to 1 hour before cooking. Remove the ribs from the marinade, letting the excess drain off, and pat dry with paper towels. Reserve the marinade.
Preheat a grill or cast-iron skillet or griddle over high heat for 5 minutes. Grill the ribs until they get caramelized and are just cooked through, 3 to 4 minutes per side.