Rub the pork with salt and let it rest overnight in the fridge.
Put the water, ginger root, garlic, green onions, and salted pork in a pot and bring to a boil over high heat.
Remove the scum and other impurities from the surface. Then cover, reduce to low heat, and let simmer for 1.5 to 2 hours.
Let the broth and pork cool completely in the pot. Strain and keep the broth and pork separate.
Let the broth cool in the refrigerator for at least a few hours or overnight, then remove the solidified fat. Also keep the cooked pork in the refrigerator so you can slice it easily later.
Also prepare the rest of the toppings (soft-boiled eggs, blanched bean sprouts, chopped green onions) before preparing the broth and noodles. Once the noodles are cooked, you'll need to add the soup and toppings right away, otherwise the noodles will become too soft, so you won't have time to prepare the toppings.
Bring the broth to a boil and add soy sauce, sake, salt, and sesame oil. Let simmer on very low heat until the noodles are ready.
Cook the dried noodles according to the package instructions. Just before the noodles are cooked, pour the broth into serving bowls.
Drain the noodles and immediately distribute them into the serving bowls.
Garnish with soft-boiled egg, bean sprouts, green onions, and pork slices.
Notes
Regarding very popular toppings for ramen: White pepper gives a bit of heat and spicy aroma, grated garlic gives a very strong garlic flavor, and chili oil gives... heat. Or soak the soft-boiled eggs in a soy sauce-based sauce to make Ajitama.