Buffy is often a central focus. Since she's the Slayer, she has to deal with any new threats or problems that arose from the Halloween events. Willow and Xander are also commonly focused on as they are Buffy's closest friends and are usually involved in whatever chaos is going on.
Often, we also see new characters being introduced. For example, a young sorcerer who Merlin takes under his wing. This new character can act as a sort of foil to Merlin, showing how much he has grown and changed. And sometimes, we might see the return of Morgana in a different form, either as a spirit guiding Merlin or as an enemy he has to face one last time. It all depends on the direction the fanfic author wants to take.
One possible plotline could be the characters dealing with the lingering effects of the Halloween chaos on their normal lives. For example, Willow might struggle with some newfound magical knowledge she gained during the Halloween events and how it affects her studies. Another could be Buffy having to face a new threat that was awakened or emboldened by the Halloween mayhem.
Naruto is often still a main focus. Since he is the protagonist of the original series, fanfic writers like to explore different versions of him. But sometimes, other characters like Sasuke also get a lot of attention. Writers might make Sasuke more of a guiding figure for Naruto in a 'renegade' way, rather than just a rival.
Obviously Naruto is the main focus most of the time. But other characters like Sasuke can also be important. Sasuke's own dark past and his relationship with Naruto can be further explored in a 'dark' context. For example, they might become rivals in a more extreme and less friendly way.
Captain America is also commonly a central character. His old - fashioned values can be at odds with the more modern - thinking Avengers. His leadership style can be both a unifying and a dividing factor among the team, much like a father figure in a dysfunctional family.
Well, in 'Harry Potter Magical Puberty Fanfic', Harry Potter is usually a central figure. After all, he is the Boy Who Lived. His experiences with magical puberty can be a great source of exploration. Hermione Granger is also commonly focused on. Her intelligence combined with the changes of puberty can lead to some interesting character development. Ron Weasley too, as his insecurities might be amplified or changed during this time. And sometimes, characters like Draco Malfoy can also be a focus, especially when it comes to how his relationships with the main characters shift during their pubertal magical growth.
Typically, Harry is the main character as his journey through different levels of magical maturity is a major draw. But other characters like Luna Lovegood can also be focused on. Her unique view of the magical world and how it changes as she matures can be really interesting to read about. Also, Draco Malfoy might be a character of interest, seeing how his upbringing in a dark - influenced family affects his path to magical maturity.
Harry Potter is usually still a main focus. After all, he's the hero of the original series. Hermione Granger and Ron Weasley are also often central characters. Their friendship with Harry and their own relationship are likely to be explored further.
Bernadette and Howard are also common focuses. Given their own relationship quirks and Howard's transformation from a womanizer to a family - man - in - training, a pregnancy can add more depth. Bernadette's pregnancy could show her taking charge even more in the relationship and family matters.
Iron Man is often a main focus. His genius and charisma make him a popular choice for fanfiction writers. They can explore his relationships with other Avengers, like his banter with Captain America.