Boil the bok choy in salt water and cut and half. Cut the cilantro to bite sizes.
Cut the beef to big bite sizes. Add water, ginger, Tokyo negi, star anise, garlic, and beef into a pot and boil. While the water is boiling, remove scums and add in the other ingredients: Soy Sauce, Shaoxing Wine, and Doubanjiang. Simmer in low heat for another 30 minutes.
Add in the tomatoes to the pot from step 2 and simmer for another 20 minutes. If there’s less water, add in some water and adjust with salt and pepper.
Remove tomato skin, star anise, Tokyo negi, ginger, and garlic from the pot. Once the beef are soft and tender, the soup is ready!
Boil plenty of water in a separate pot. Cook the udon noodles, following the instructions in the package. Once the udon is done cooking, drain well. Place the udon in a bowl and pour in the soup from Step 4. To finish, top with bok choy and cilantro. Enjoy!