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An interest bit of evidence while I was perusing for something else. This was a sign in the Grass gym city seen from far away. Most of it is confusing, and we would need to see it closer, but one of the letters is recognizable, the first one. This is likely the sign telling you what the town/city name is, but for simplicity, it has to be the same sign for every location. Note that both city and town are four letter words, but that would be no help regardless since it does have to be the same sign everywhere. As for romaji, it would be written as taun or shiti, only one of which is a four letter word. (unless they want to spell sh with one letter for some reason) Only one of those is composed of four different letters, though. (again, it makes no difference in English)
This can either mean we're on a wild goose chase, or they chose one word to stand for all towns and cities for some reason. If so, it leaves us with only a few possibilities for what one letter is.