I'm not sure as I haven't read the novel. But usually, the main characters are those who drive the plot forward. They could be the ones who are most affected by the 'darkness' in the story.
The main theme could be about the struggle against inner demons or difficult situations. It might deal with how characters are affected by the 'darkness' in their lives, perhaps it's about moral dilemmas, or the fight to overcome hardships.
Since it's a novel about 'darkness', there could be a character who is initially innocent but gets drawn into the dark world. There may be a mentor - like figure who tries to guide this character out of the darkness. Or perhaps a group of characters with different motives, some good and some bad, all interacting in the setting of this 'darkness' that the novel portrays.
I'm not familiar with this particular novel. However, it might have a group of characters. There could be a mentor figure who guides the others through the darkness, and a villain who is somehow associated with or causing the darkness in the story.
Well, in such a novel, there could be a group of characters. For example, a young adventurer who is the central figure, and his or her friends or companions. One of them might be a strong - willed person who encourages the others when they are in the grips of the 'darkness'. Another could be a more timid character who gradually grows stronger throughout the story.
Most likely, Ruby, Weiss, Blake, and Yang will be main characters as they are central to the RWBY universe. They might be joined by other characters like Jaune or Pyrrha who could play important roles in the story of the fanfic.
I'm sorry I don't know this short story, so I can't tell you the main characters. But typically in a short story, the main characters would be those directly related to the torn invitation incident. It could be the person who received the invitation, the sender, or someone who has a strong reaction to the torn state of the invitation.
The main character is Marlow. He is the narrator of the story and his journey into the Congo forms the core of the novel. Kurtz is another important character. He is a man who has become a sort of demi - god in the Congo, representing the extreme of what European influence can become in the African context.
Since I haven't read the novel, I can't tell you the exact main characters. But they could be a brave hero who has to face the tempting darkness, or a group of adventurers.
In the 'hero of darkness novel', the central character would be the hero of darkness himself. He might be joined by a group of comrades, each with their own unique abilities and backstories. One of them could be a wizard who specializes in the study of dark magic, not in an evil way but in a way to understand it better to help the hero. Another could be a warrior who has a past with the hero and is now by his side to fight against the common enemies. And there could be a female character who is a seer, able to foresee events related to the hero's journey through the darkness.
I'm not sure specifically as I haven't read the 'Edge of Darkness Novel' in detail. But usually, in a novel with such a title, there could be a protagonist who is likely to be a complex character, perhaps someone with a troubled past or a strong will. There might also be an antagonist who represents the source of the 'darkness' in the story.