Preheat your oven to 250°F.
Heat a large Dutch oven or wide stock pot over medium-high heat. Make sure the pot is big enough to fit all the oxtails in one layer.
Add the oil and sear the oxtail on each side for 2 minutes until brown. Remove the oxtails to a plate.
Add the onions, garlic, and ginger to the pot. Cook for 2 minutes until softened.
Add the Chinese cooking wine, apple juice, soy sauce, brown sugar, rice vinegar, and dark soy sauce, and star anise.
Add back the oxtail and bring to a boil. Cover the pot with a lid (or tinfoil) and transfer to the oven. Cook for 2 hours, flipping the oxtail once in between.
Remove the pot from the oven and set it on the stovetop. Increase the oven temperature to 300°F.
Add daikon to the pot, making sure the pieces are fully covered in the liquid. Bring the liquid back to a boil on high heat. Cover and transfer back to the oven. Continue cooking for another hour.
If the daikon is still not soft, just keep cooking it for a bit longer. Enjoy!