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.
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.
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.
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.
The relationship would become extremely complex. Harry would be confused and conflicted. He's been taught all his life that Voldemort is pure evil, but now he's been saved by him. Voldemort, on the other hand, might start to see Harry in a different light, perhaps as a tool or as someone with whom he can form an unusual bond. It would be a relationship full of mistrust on Harry's part and manipulative intentions on Voldemort's.
At first, it would be extremely tense. Voldemort would be highly suspicious of Harry's motives. Harry, on the other hand, would be very cautious as he is approaching his mortal enemy. But as they start to interact more, there might be a grudging respect that develops if they find they have common goals.
The relationship would become extremely complex. Harry would no longer be able to simply see Voldemort as pure evil. He would be in a state of confusion and moral dilemma. Voldemort, on the other hand, might start to view Harry as a more interesting pawn rather than just an enemy to be killed. They could develop a strange sort of respect for each other, at least on a surface level.
In this fanfiction, Voldemort's character is explored in a way that challenges our traditional view of him. His seeing Harry abused might make him reevaluate his relationship with Harry. He may start to see Harry not just as the Boy Who Lived who he wants to defeat, but as a person who has suffered, much like he might have in his own way. Harry, on the other hand, is stripped of some of his heroic facade. His abuse makes him more relatable in a sense. We can see his pain and how it affects his actions and decisions, and also how he reacts to Voldemort's new - found interest in his situation.
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, in such a fanfiction, it could completely flip their relationship. Maybe Harry realizes that Voldemort has some hidden motives that are not entirely about killing him. It might be that Voldemort sees some value in Harry that he wants to use for his own gain, rather than just destroying him like in the original story.
Harry might develop from being a purely good - vs - evil thinker to someone who understands the complexity of Voldemort. He could become more cynical about the wizarding world's black - and - white view. Voldemort, on the other hand, could develop a strange sort of softness towards Harry. Maybe he starts to protect Harry in his own twisted way.