Since I don't know the specific 'as black as night fanfic', it's hard to say. It could be an original character created by the fanfic writer or it could be characters from an existing series that the fanfic is based on.
There's no way to be certain without reading the fanfic, but it might feature a protagonist who is somehow associated with the 'black as night' concept. Maybe a person with a dark past or a special ability related to the night. There could also be an antagonist who thrives in the darkness and tries to oppose the main character.
In a 'as black as night fanfic', the main characters could vary greatly depending on the genre and the plot. If it's a horror - themed fanfic, the main character could be a victim trying to escape from a terrifying entity that lurks in the blackness of the night. Or if it's a romance, it could be two lovers whose relationship is somehow intertwined with the mystery and allure of the night.
It could be a young protagonist who is brave but also has a lot to learn. This character might be the central figure in the story.
I don't know the specific main characters in 'night dragons fanfic' as it depends on the content of the fanfic. It could be the night dragons themselves, perhaps with names like Nocturne or Shadowscale.
Typically, the main characters are the brothers themselves. Each brother has his own unique personality, like the eldest brother who might be more responsible and the younger ones who could be more carefree or adventurous.
Since I don't know the exact 'the night dragons fanfic', it's hard to say. But likely, the main characters would be the night dragons themselves. There might also be other characters like dragon hunters or magical beings that interact with the night dragons.
There might be a rookie in the squadron who is also a main character. This character could be learning the ropes, making mistakes, but also showing great potential. Their journey of growth within the squadron can be a central part of the fanfic.
I'm not sure specifically as it depends on the fanfic. But it could be a young girl who has a special connection with the black roses. Maybe she can communicate with them or has the power to make them grow.
I think there might be some original characters created specifically for the fanfic. They could play important roles in either helping or opposing the Archer. Maybe there's a sidekick character who provides some comic relief or a powerful antagonist who challenges the Archer at every turn.
It could be two best friends. They decide to go on a spontaneous road trip for one night and two days. They share stories, laugh, and have a bit of an argument when one wants to take a different route. But in the end, they come out stronger as friends.
Another possibility is that it could focus on some of the recurring characters from the show but give them a more prominent role. For instance, Castiel could be a main character in this fanfic, and the 'back in black' concept could be related to his journey or a new aspect of his powers.
Sebastian Michaelis could also be a main character in some fanfics. His demonic nature and loyalty to Ciel can create interesting interactions with Vintaker. Their different motives and abilities can lead to intense confrontations or unexpected alliances in the fanfic.