Soak ribs in a large bowl of cold water to drain residual blood, changing water as needed, about 1 hour. Drain.

Mix soy sauce, 4 cloves minced garlic, sesame oil, and pepper together in a bowl. Add sliced radish.

Place ribs in a large pot and cover with water. Add onion half, 2 cloves garlic, and ginger. Bring to a boil, skimming any foam that floats to the top, about 15 minutes. Drain, discarding onion, garlic, and ginger.

Rinse ribs and return to the pot. Cover with fresh water. Bring to a boil; reduce heat and simmer until tender, about 20 minutes.

Stir radish mixture into the pot. Cook until flavors combine, about 10 minutes. Add noodles and scallions; cook until noodles are tender, 2 to 4 minutes.

Ladle soup into bowls. Garnish with egg strips and toasted sesame seeds.