Prepare the sukiyaki broth by combining soy sauce, mirin, sake, sugar, and water in a bowl. Stir until sugar dissolves and set aside.

Arrange all prepared vegetables, tofu, and thinly sliced beef on a large platter for easy access during cooking.

Cook udon noodles according to package instructions, drain, and set aside.

Heat a large shallow pot or sukiyaki pan over medium-high heat. Add vegetable oil and sear a few slices of beef until browned, about 30 seconds per side.

Pour in half of the sukiyaki broth and bring to a gentle simmer. Add napa cabbage, shiitake mushrooms, and tofu to the pot.

Continue simmering for 8-10 minutes, adding spring onions and enoki mushrooms halfway through cooking.

Cook beef slices in the simmering broth in batches, ensuring each slice reaches an internal temperature of 63°C for medium doneness or 71°C for well done, approximately 1-2 minutes per batch.

Add cooked udon noodles to the pot in the final 3 minutes to warm through and absorb flavors.

While sukiyaki simmers, crack one egg per person into individual small dipping bowls and beat lightly with chopsticks until silky smooth.

Serve the hot sukiyaki directly from the pot, allowing each person to dip cooked ingredients into their beaten egg before eating. Add more broth as needed and continue cooking remaining ingredients at the table.