Soak ribs in cold water for 15 minutes (See Note 2). Rinse and add to a stock pot of boiling water. Return water to boil and flash boil 5 minutes. Drain and set ribs aside.
In a blender add the onion, pear, garlic, ginger, soy sauce, mirin, apple juice, sugar, red pepper flakes and black pepper. Puree until smooth.
Transfer short ribs to Instant Pot, pour sauce over, and if needed, add enough water to cover. Close lid and cook on Pressure Setting for 45 minutes on High. Allow for Natural Release.
Remove lid. Using tongs, remove ribs, cover with foil and set aside. Transfer sliced carrot and radish to the pot, stir and press Saute setting for 15 minutes. In last 5 minutes add the green onions (stir to mix). Vegetables with be firm tender and sauce will thicken.
Serve ribs with vegetables and sauce poured over. I like to also serve along side some steamed rice.