One of the most interesting characters could be an original character created by the fanfiction author. For instance, a wizard who has been secretly studying Horcruxes for years and has unique knowledge that helps Harry. He could be an outcast from the wizarding community but has a heart of gold.
The last Horcrux itself, if given a sentient form in the fanfiction, can be an extremely interesting character. It could have its own motives, like trying to survive not just for Voldemort's sake but for its own existence. It might try to bargain with Harry or his friends, offering knowledge or power in exchange for its life.
Harry Potter would surely be one of the main characters. Since it's about the last Horcrux, he's the one on the mission to destroy it. His friends, like Hermione and Ron, would likely also be main characters as they usually accompany Harry on his adventures.
One interesting plot twist could be that the last Horcrux is not an object but a person no one suspected. For example, it could be a seemingly innocent bystander who has been under Voldemort's control all along without anyone realizing.
In a 'harry potter and the last horcrux fanfic', it may center around the significance of the last Horcrux. It could depict the emotional and mental state of Harry as he approaches the end of his long journey. There could be unexpected twists, like the Horcrux being hidden in a place no one suspected. It might also expand on the lore of Horcruxes, for example, by showing different ways to detect or destroy them that were not mentioned in the original series.
Harry Potter himself is often a central character. Since he was the one destined to defeat Voldemort and destroy the Horcruxes in the original story, many fanfictions continue his journey with Horcruxes in new and different ways. Hermione Granger also features prominently. Her intelligence would be crucial in understanding the nature of Horcruxes and finding ways to deal with them.
Obviously, Harry Potter is one of the main characters since he is the one who is a Horcrux. His friends Ron and Hermione are likely to be main characters as well, as they are always by Harry's side in the original story and would play important roles in dealing with this new situation.
In many fanfictions, Neville Longbottom might also play a significant role. He has grown into a powerful wizard by this point in the story. His knowledge of Hogwarts and its secrets could be crucial in the search for the seventh horcrux. He could be the one who discovers a hidden passage that leads to the location of the horcrux.
Yes, in some fanfiction, Harry Potter is considered a Horcrux. This concept adds an interesting twist to the original story, exploring different aspects of magic and the connection between Harry and Voldemort.
One consequence could be that his connection to Voldemort becomes even stronger. This might lead to him being able to sense Voldemort's actions and thoughts more clearly, but also make him more vulnerable to Voldemort's attacks on his mind. Since the Horcrux is a part of Voldemort's soul, it could also start to influence Harry's personality, making him more aggressive or moody at times.
One interesting concept is the idea of creating new Horcruxes. In some fanfictions, a character might attempt to create a Horcrux in a different way than Voldemort did, perhaps using a more unique object or spell. Another concept could be the destruction of Horcruxes in unexpected ways. For example, a fanfic might explore if a Horcrux could be destroyed by a powerful emotion rather than a specific magical weapon.
One of the most interesting characters can be the shifter protagonist themselves. They bring a new dynamic to the story. For example, a shifter who can turn into a phoenix might have the power of rebirth and be a symbol of hope. Another interesting character could be a wizard who befriends the shifter and helps them navigate the wizarding world, like a young Hermione - type character using her intelligence to understand the shifters' unique situation.