Season ribs lightly with salt and pepper. Whisk ponzu, rice vinegar, tamari, honey, chili garlic sauce, ginger, and sesame oil. Coat ribs well and marinate for at least 1 hour or up to overnight.
Heat oven to 300°F (150°C). Place ribs on a foil-lined sheet or baking dish, cover tightly, and bake 2–2½ hours until tender.
Pour marinade into a saucepan and bring to a simmer for 5–7 minutes. Stir in the cornstarch slurry and cook until glossy.
Brush ribs generously with glaze and broil 3–5 minutes until bubbling and slightly charred.
Let rest 5 minutes, then slice between bones and brush with extra glaze.