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.
In the 'Back in Black' story, the main characters are the members of AC/DC. Angus Young with his iconic schoolboy look and his amazing guitar skills. Brian Johnson, who stepped in as the lead singer after Bon Scott's death and played a crucial role in making the 'Back in Black' album what it is.
Since I don't know the 'Back in Black Novel' well, it's hard to say exactly. But there could be a strong - willed protagonist who is at the center of the story, maybe someone who has a troubled past.
The main characters in the Cindy123 Supernatural Fanfic could very well be the Winchester brothers. They are iconic in the Supernatural world. But depending on the creativity of the writer, there could be other characters like angels or demons that play significant roles. Maybe there's a human character who has a special connection to the supernatural, like being a seer or having some sort of magic ability that was given to them. It all depends on how Cindy123 has developed the story.
Most likely, Marty McFly would still be one of the main characters. He's the central figure in the original movies and would probably play a major role in the fanfic set in 2015. Doc Brown would also be there, as he's the inventor of the time - travel technology and Marty's mentor. There could also be Biff Tannen or his descendants, as they often cause trouble in the 'Back to the Future' universe.
Deadpool is obviously the main character. He's the one in the black suit driving the story forward with his antics.
The 'back in black' part might imply a certain style or theme. Maybe it's about a character coming back in a cool, edgy way, like with a new look or attitude. It could also be related to a specific plot device where something that was lost or gone comes back in a big, impactful way.
Since I haven't read it, I can't say for sure. But it could potentially feature the main characters from the Supernatural series like Sam and Dean Winchester, Castiel, or Crowley, if it stays true to the source material in terms of character inclusion.
Since I don't know the specific 'black sky fanfic', I can't say who the main characters are. They could be original characters created by the fanfic author, or they might be characters from an existing franchise that the fanfic is based on.
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 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.