Since I haven't read the specific gold coin story, I can only guess. There could be a protagonist, perhaps a young adventurer who discovers the gold coin during his journey. There might be an antagonist, like a cunning old miser who wants to take the gold coin away from the adventurer. And there could be other supporting characters such as the innkeeper where the adventurer stays and who gives him some advice about the gold coin, or a wise old man in the village who knows the true value and the history of the gold coin.
In some 'city of gold stories', there could be local guides or natives who play important roles. They might know some secrets about the location of the city. The main characters also could include greedy conquistadors who were more interested in looting the gold than understanding the culture of the place. And sometimes, there are wise elders in the story who try to protect the city of gold from being discovered by the wrong people.
Yang is also very popular. Her strong - willed and fearless nature provides great material for fanfic writers. They might write about her in intense combat situations or her relationships with other characters, such as her sisterly bond with Ruby.
There might be a mysterious side character that becomes popular in the fanfic. Maybe they have a hidden past or special powers that are gradually revealed as the story progresses. Fans are always intrigued by such characters as they add an element of mystery to the narrative.
I don't have enough information to know the main characters. It could be original characters created for the fanfiction, or it could be characters from the original source material that the fanfiction is based on.
The main character is probably the king, as the name 'king gold story' implies. There could also be a character who tries to steal the king's gold. Maybe there is a magician or a thief who plays an important role in the story. Another possible main character could be a poor person whose life gets affected by the king's gold, either in a positive or negative way.
Since I don't know the exact 'gold watch story', it's hard to say. But it could be a grandfather who owns the gold watch and his grandson who inherits it.