To prepare sauce: in a small saucepan, whisk together 1 cup water, soy sauce, mirin, sake, and sugar over high heat. Bring to a boil. Reduce heat to medium and simmer for 15 minutes.

To prepare the negimaki: wrap the beef around the scallions and secure with a skewer. To prepare the meatballs: combine the ground beef, onion, red pepper, salt and pepper to taste. To prepare the stew: add the negimaki, meat balls, beef bones, tofu, nappa cabbage, shiitake mushroom, enoki mushroom, and udon noodles in a pot and pour the sauce over all the ingredients. Bring it to boil.

Lower heat and simmer for 20 minutes, or until meat is cooked through.