In this fanfic, Voldemort's reaction would be multi - faceted. Initially, he would be stunned by the revelation. He has always considered Harry as his nemesis, but now he realizes that Harry is also a part of his own dark magic. This could lead to him being more cautious in his approach. He might be hesitant to attack Harry as brutally as before, because he doesn't want to accidentally destroy the Horcrux. Instead, he could start to use more psychological warfare, trying to get inside Harry's head and manipulate him into doing his bidding.
His reaction would likely be very different. At first, he might be angry that he didn't know this before. But then, he could start to see opportunities. He may think that if he can somehow control Harry as a Horcrux, he can gain more power. So, he might change his strategy from simply trying to murder Harry to trying to subdue him in a different way.
Well, it depends on how the author writes it. Maybe Voldemort would initially be in disbelief. But once he accepts it, he could start to manipulate Harry in different ways. He might think that by controlling Harry, he can control the Horcrux within him. This could create some really interesting plot twists where Harry has to resist Voldemort's attempts at a much deeper level than just physical attacks.
Well, in such a fanfiction, Harry being Voldemort's snake might initially make their relationship more of a master - servant one. But as the story progresses, Harry could start to resist Voldemort's control, leading to a more adversarial relationship.
Often in fanfiction, their relationship can change drastically. They could end up as allies, which would require both of them to change. Harry would have to see past Voldemort's evil deeds, and Voldemort would have to let go of his hatred for Harry. This exploration of character change makes fanfiction so interesting.
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.
Harry could become more powerful in a way that scares his friends. Voldemort's training might focus on the Dark Arts, which are powerful but dangerous. This could change Harry's magic style. He may become more solitary as his new skills and knowledge set him apart from his Hogwarts friends who follow a more traditional path of magic.
Well, a major aspect is the impact on the overall story arc. In these fanfictions, the fight against Voldemort takes on a whole new meaning. Harry being a Horcrux means that his very existence is intertwined with Voldemort's. There's also the element of secrecy and revelation. How and when the other characters find out about Harry being a Horcrux can be a crucial part of the plot. And, of course, there's the magical mechanics of what it means to be a Horcrux. How does it affect Harry's magic? How can it be destroyed without killing Harry? These are all things that are often explored.
At first, it would be extremely tense and full of suspicion. Harry would be very wary of Voldemort's motives for protecting him. Voldemort, on the other hand, might be impatient with Harry's lack of trust.
Harry often becomes more conflicted. He has always seen Voldemort as the ultimate evil, but now being mates, he has to re - evaluate his views. He might start to see the humanity in Voldemort, which makes him question his own beliefs and actions in the fight against the Dark Lord. For example, he may hesitate in battles more than before.
He might become more vulnerable. Usually seen as a powerful and cold - hearted villain, losing his lover could expose a softer side. He could start to show emotions like sadness or regret that he has never shown before.
One popular 'Harry is Voldemort's Horcrux' fanfiction is 'The Horcrux Within'. It delves deep into how Harry's new status as a Horcrux affects his relationships with his friends, especially Hermione and Ron. It also shows his internal struggle as he tries to come to terms with this dark connection to Voldemort.