Well, aside from Harry Potter and Acheron, other characters from the original 'Harry Potter' series often play important roles too. Hermione and Ron might be there to support Harry in his new adventures with Acheron. Dumbledore could also make appearances, perhaps guiding Harry and Acheron in their journey, especially if they are dealing with something that has to do with the greater good of the wizarding world.
Well, clearly Harry Potter and Acheron are main characters. Harry is the boy wizard we all know from the original series, and Acheron brings in his own set of characteristics and powers from his own lore. Hermione and Ron could also be important characters as they are Harry's closest friends and often get involved in his adventures in fanfictions too.
Since I haven't read the Acheron novel, I can only guess. There could be a strong - willed hero or heroine as the main character. Maybe there's also an antagonist who constantly opposes the main character's goals. There might also be some side characters that provide support or add complexity to the story.
I don't know for sure as I haven't read it. But I assume Acheron is one of the main characters. There might be others who interact with Acheron and play important roles in the story, like his allies or enemies.
For Harry, you can focus on his growth beyond what we see in the original series. Maybe he becomes more cynical after all he's been through, and Acheron challenges his views. For Acheron, explore his past more deeply in the context of the fanfiction. Have Harry learn about his traumas and help him heal in some way.
There might be a character who is a rival to Harry. This rival could have different motives, like jealousy or a thirst for power. They constantly challenge Harry, which makes for an interesting dynamic. Also, there could be a magical creature character that befriends Harry. For example, a phoenix that can provide help and support in difficult situations, and its own personality and abilities add an interesting aspect to the story.
One interesting plotline could be the exploration of a new magical bond between Harry Potter and Acheron. Maybe they discover a hidden magic that only they can access together, which helps them face a new dark threat in the wizarding world.
You can try looking on popular fanfiction websites such as Archive of Our Own (AO3) or FanFiction.net. These platforms have a large collection of fanfictions, and you might be able to find the one you're looking for by using the search function and typing in relevant keywords like 'Harry Potter' and 'Acheron'.
Acheron is likely to be one of the main characters. But there may be others who are also important, like his comrades among the dark hunters.
One interesting 'Harry Potter Acheron' fanfiction could be one where Acheron has some sort of magical connection with Harry Potter that was hidden for years. Maybe Acheron has the power to unlock a hidden potential in Harry that no one else knew about.
Well, clearly Vionery is one of the main characters. Depending on the story, Harry Potter himself might also be a central figure, as he often is in most Hogwarts - related fanfictions. Hermione Granger could also be involved, using her intelligence to assist Vionery in her adventures or studies at Hogwarts.