I think Voldemort would be the most interesting. We rarely get to see his perspective in the original series. In a fanfic where Harry talks to him, we might get to see a more complex side of Voldemort. Maybe he'll show some vulnerability or a different motivation than just pure evil. It could be really fascinating to see how he reacts to Harry's words and if he is capable of any change.
It could be both Harry and Voldemort equally. Harry because he is the hero trying to reach out to the ultimate villain. His character growth and the development of his ideas during the conversation would be interesting to follow. But Voldemort too, as his reactions to Harry's attempts at communication could be very unpredictable. He might show a side of himself that we never expected, and his internal struggle (if there is any) between his dark desires and Harry's words would make him a very engaging character.
One possible plot could be that Harry tries to reason with Voldemort about the futility of his dark ways. He might talk about how much destruction Voldemort has caused and how many lives have been lost. Harry could also try to appeal to any remaining shred of humanity in Voldemort, perhaps by bringing up his own orphan status and how they both lost their parents in a way, though for very different reasons.
It's hard to say for sure. Given the rather unusual concept, it might be difficult to find one with a widely appealing plot. But in the vast world of fanfiction, there could be some hidden gems. Maybe a plot where Harry, through some magical accident, starts to see things from Voldemort's perspective and tries to'spread' his new - found understanding among others in the wizarding world.
One possible plot could be Voldemort brainwashing Harry to turn against his friends at Hogwarts. Harry might start acting strangely, like isolating himself from Ron and Hermione. Another plot could involve Voldemort using the brainwashed Harry to steal important magical artifacts from the school. Maybe Harry is made to believe that these artifacts are rightfully Voldemort's and that he's on a noble mission.
One interesting concept is when Voldemort cheats by infiltrating Harry's dreams. He can manipulate the dream world to make Harry doubt himself or give away secrets. It adds a psychological aspect to their conflict. Another is when he cheats by using ancient magic that no one expects. This often leads to Harry having to research and learn new magic quickly to counter it.
One interesting fanfic could be where Voldemort cheats in a magical duel against Harry by using a forbidden spell that gives him an unfair advantage. In this kind of story, Harry might have to figure out a way to counter this cheating without breaking the rules himself.
One interesting plotline could be Voldemort being redeemed. It's a really different take as in the original books he's pure evil. But in fanfic, some writers explore what if he had a change of heart.
Well, in the 'harry talks about the dursleys fanfic', it might be fascinating to see how Harry describes their daily routines. It could give us a deeper understanding of the Dursleys' world from Harry's point of view. He might talk about how their obsession with normalcy affected him and how he coped with it during his time living with them.
He becomes more conflicted. Knowing he's Voldemort's son, he's constantly in turmoil about his true nature. His confidence might waver as he wonders if he's capable of the same evil as his father.
Well, in these fanfics, Harry's ability to talk to snakes can show his connection to a more primal and often misunderstood part of the wizarding world. It can highlight his empathy, as he tries to understand the snakes' point of view. For instance, he might realize that snakes are not all evil just because they are often associated with dark magic in the wizarding world.
Well, in such a fanfic, the power dynamics could be really fascinating. Since Voldemort is extremely powerful, Harry as his son might inherit some of that power in unique ways. This could lead to new spells or abilities that we haven't seen in the original series. Also, the whole idea of the prophecy might be turned on its head. Instead of being the one注定 to defeat Voldemort, he could be seen as a potential successor to his dark reign. But then, his mother's love which was so crucial in the original might still have a strong influence on him, making him reject the dark path.