It's hard to say for sure without reading the fanfic. However, if the fish cake affair has something to do with a mystery, it could be that a detective - like character, maybe someone inspired by the shinobi skills in Naruto, is the main character. They could be investigating the strange happenings around the fish cakes. Or maybe it's a character who has a secret love for fish cakes and their actions in trying to obtain or protect them make them the main character in this 'naruto fish cake affair fanfic'.
Since it's a fanfic, it could really vary. But likely Naruto himself would be one of the main characters, as it's in the Naruto universe. And perhaps some of his friends like Sasuke or Sakura could also be involved if the fish cake affair somehow impacts their relationships or the village as a whole.
A 'naruto fish cake affair fanfic' could potentially revolve around a comical or dramatic event. For example, it could be that Naruto discovers a special kind of fish cake that has some sort of magical or mysterious property. And then an 'affair' in the sense that there are conflicts or intrigues among the characters regarding this fish cake. It could also be a love - triangle - like situation where the fish cake is somehow in the center of it all, in a very strange and fan - fic - like way.
Obviously Naruto would be one of the main characters. He could be joined by his friends like Sasuke and Sakura. And of course, the tuna fish would be a central character as well, whether it's a regular tuna fish with a special role or a magical, anthropomorphic tuna fish.
I'm not entirely sure as I haven't read every 'the affair fanfic' out there. But usually, there would be characters involved in the affair, perhaps a married person and someone they are attracted to.
Since I don't know the specific 'christmas cake story', it could be a baker as a main character. The baker who painstakingly creates the perfect Christmas cake.
I don't know as I haven't read this novel. But usually, main characters are those who drive the story forward. They could be the ones with the most complex personalities or the ones with the biggest goals in the story.
There's no way to be certain without reading the novel. But perhaps there's a protagonist who has just inherited the recipe for the black cake and in the process of making it, discovers a whole new side to their family's history. There could be other characters like siblings or neighbors who play important roles in either helping or hindering the protagonist's exploration of the black cake's significance.
It's possible that the main characters are people from different backgrounds but are united by their love or hatred for the black cake. There could be a local baker who is known for making the best black cake in town and a customer who has a special connection to the cake. As the story progresses, their lives become intertwined through the black cake and their individual stories unfold.
There could be many possibilities. Maybe it's an old woman who has been making the black cake for decades and she is one of the main characters. Or it could be a young girl who is learning the recipe of the black cake from her grandmother, so both of them would be main characters. Also, if the black cake is part of a community event, the organizer of that event could be a main character in the story related to the black cake.
In some Naruto fish cake fanfiction, the fish cake could be a symbol of a hidden power. For example, it could be revealed that a certain type of fish cake was created long ago by a powerful ninja clan, and Naruto stumbles upon the secret of this fish cake during one of his adventures. He then has to protect the fish cake from villains who want to use its power for evil.
I don't know as I haven't read it. Maybe members of the Mitford family are the main characters.