I'm not sure specifically which fanfic you're referring to. There could be various interpretations of Annie January's character in a Boys - Marvel Universe crossover fanfic. Maybe she could have unique powers or relationships that differ from the original stories.
One possible plot could be Annie January trying to expose the seedy underbelly of the Boys' version of the superhero world while still maintaining her own heroic image. She might team up with some of the more morally ambiguous characters in The Boys to achieve this.
The Avengers originated in Marvel Comics. Marvel has developed a vast universe of characters and storylines, and the Avengers are a key part of it. Their adventures have been adapted into various forms of media, including movies and TV shows.
Captain Marvel is Carol Danvers. She gained her powers through an interaction with alien technology and has become a powerful hero in the Marvel universe.
Marvel justifies Marvel Comics 1000 by presenting it as a celebration of their rich history and a platform to introduce fresh and exciting story arcs. It could also be a strategic move to attract new readers and reignite the passion of long-time fans.