When you finish a bowl of ramen in Japan, it is perfectly normal to leave a fair amount of broth behind. Many people eat all the noodles and toppings, take a few more sips of the soup, and stop there.
Drinking every last drop of ramen broth is not a requirement of Japanese dining etiquette.
On the other hand, finishing all the broth does not automatically make someone seem more polite either. People might simply think, “They must have really liked it,” or “They were probably very hungry.” In most cases, it is just a matter of personal preference.
So there is no major etiquette penalty for leaving the broth, and no special etiquette reward for finishing it. You can drink a little more after the noodles are gone, stop when you have had enough, or finish the whole bowl if you genuinely want to.
In fact, people in Japan may sometimes say things like, “Isn’t that too much salt?” or “You probably shouldn’t drink all the soup.” Ramen broth can contain a substantial amount of sodium, and Japanese public-health guidance on reducing salt intake commonly recommends leaving some or all of the soup from noodle dishes.
There is therefore no need to think that finishing the broth is a way of showing respect to the cook. Appreciating the food and leaving some soup are not contradictory.
Of course, if someone drinks every last drop, others may assume that they really enjoyed the broth. But that is not because finishing it is the “correct” thing to do. It simply means they wanted to keep drinking it.
In Japan, leaving ramen broth or finishing it usually makes little difference in terms of manners. Drink as much as you want. And if you are watching your salt intake, leaving the rest is completely normal.
