Prepare the Short Ribs: Trim excess fat from the short ribs and rinse them under cold water. Pat them dry with paper towels.
Marinate the Ribs: Combine soy sauce, brown sugar, mirin, garlic, onion, sesame oil, and ginger in a large bowl. Add short ribs, coating each piece well. Refrigerate for at least 2 hours.
Sear the Ribs: Remove ribs from marinade and sear them in a hot pot or Dutch oven until browned on all sides.
Braise the Ribs: Add marinade and water to the pot, then bring to a boil. Reduce heat, add carrots and daikon radish. Cover and braise for about 2–2.5 hours until tender.
Finish and Garnish: Add green onions and simmer for 10 minutes. Serve with toasted sesame seeds.
Notes
Refrigerate leftovers for up to 3 days or freeze for up to 3 months. Reheat gently with added water if necessary.