Since it's a Naruto - related fanfiction, Naruto himself is most likely one of the main characters. There could also be his friends like Sakura and Kakashi. Maybe Sasuke would be involved too if the promise has something to do with their relationship.
I'm not sure exactly who the main characters are in 'naruto no promise fanfiction'. But if it's based on the Naruto universe, in addition to Naruto, characters like Jiraiya could be important. Jiraiya was Naruto's mentor, and if the promise is related to Naruto's growth as a ninja, Jiraiya might play a big role. Also, characters from Naruto's village such as Iruka Sensei could be main characters depending on the nature of the promise.
It could be two best friends. They've been through a lot together and the forgotten promise between them creates a rift that they need to overcome. For example, they might have promised to always be honest with each other, but one of them broke it unknowingly, leading to misunderstandings.
Since we don't have much information about the 'The Promise' novel, the main characters could be a group of people. Maybe it's a family where one member makes a promise to the others, and they all play a part in either helping or hindering the fulfillment of that promise. It could also be two lovers where one makes a promise to the other, and their relationship is built around that promise.
Since we don't have details about this specific story, the main characters could be various. There might be an elderly Indian sage who gives a promise of wisdom or guidance. Or perhaps a group of Indian women who make a collective promise to preserve their cultural heritage in the face of change. There could also be a character who is an outcast in the Indian community and makes a promise to redeem himself.
I'm not entirely sure as I haven't read it recently, but typically Potok's novels have characters that are part of a religious or cultural community. There might be a young protagonist who is grappling with the expectations and promises associated with that community.
Since I don't know the exact 'the promise ghost story', it's hard to say. But it could be the ghost itself as a main character, and perhaps the person to whom the promise was made or the people affected by the ghost's presence.
Typically in a fanfiction with such a title, there would be a boy and a girl as main characters. The boy is the one making the promise. They could be original characters created for the fanfiction, or they could be existing characters from the Harry Potter series, like Harry and Hermione or Ron and Ginny, with a new take on their relationship through this promise.
A mysterious figure from the captain's past could be a key character. Maybe this person was involved in the events that led to the promise in the first place. They could reappear and try to either help or hinder the captain in keeping the promise. Also, a young crew member who looks up to the captain could be important. Their naivete and admiration could add an interesting dynamic as they try to understand the weight of the captain's promise.
There could be a hero - like character who is bound by the blood promise. Maybe there's also an antagonist who tries to stop the protagonist from fulfilling the promise. And perhaps some side characters who help or hinder the main character along the way.
I don't know who the main characters are in 'the word of promise christmas story' as I haven't read it.
Since I don't know the details of the story, it's likely that the main characters are the king and the baker. There might also be other characters like the king's advisors who could be involved in the promise - either in making it or in trying to influence it in some way.