Rinse each flanken cut short rib under cold water to wash off any bone dust from the saw. Lay them out on paper towels and dry them really, really well.
Combine the soy sauce, salt, brown sugar, mirin, sesame oil, Asian pear, kiwi, onion, garlic, ginger, and black pepper in a blender. Blend for 1 minute or until completely smooth.
Lay all the ribs in 2 layers in a 9x13 baking dish. Pour the blended marinade over them and brush every piece so it's heavily coated on both sides. Cover tightly with plastic wrap and refrigerate for 12-18 hours.
Heat Grill to 450-500F to start.
Right before the meat goes on, spray or wipe the grates liberally with oil, then lay each rib on the grill.
Open the lid, brush the top side of each rib with fresh marinade, then flip. Close the lid for 1-2 minutes. Open, brush, flip again. Repeat this cycle roughly 3 more times.
Pull the ribs off the grill and let them rest for 5 minutes on a cutting board. Cut with scissors between the bones into bite-sized pieces and serve immediately with white rice and kimchi.
