The plot might go like this. Harry is adopted by Voldemort and is made to believe that the wizarding world outside is full of enemies. But as he gets older, he discovers the truth about his parents' death and Voldemort's true nature. He then has to struggle with his loyalty to Voldemort who raised him and his sense of justice. He could use his unique position to gather intelligence about Voldemort's plans and eventually turn against him to save the wizarding world.
Harry's character would be very complex. He'd likely start off confused, as he's growing up with Voldemort. He might be conflicted between the dark teachings he receives and his own innate sense of right and wrong. As time passes, he'd probably become more rebellious against Voldemort's ideas, especially when he starts to learn about the real world outside Voldemort's influence.
In such a fanfiction, Harry might be raised with a very different set of values. Voldemort could try to mold Harry into his own image, perhaps teaching him dark magic. But Harry might also secretly hold on to his own sense of good. For example, he could use the knowledge Voldemort gives him to ultimately turn against him.
In this fanfiction, the relationship between Harry and Voldemort would be full of contradictions. Voldemort adopts Harry for his own purposes, but Harry has his own will. In the beginning, Harry may be forced to follow Voldemort's orders out of fear. As time passes, he might start to question Voldemort's actions and ideology. Voldemort, seeing Harry's growing independence, could become more controlling. This could lead to a cycle of rebellion and suppression in their relationship. Harry may also find some common ground with Voldemort in their shared loneliness or desire for power, which would add more layers to their complex relationship.
If Harry Potter was adopted by Voldemort in fanfiction, it would be a very strange and complex situation. Voldemort is a very evil character, but he might see Harry as a tool or an heir. Harry could be exposed to the darkest magic and the inner workings of the Death Eaters. However, Harry's own strong will and the influence of his parents' sacrifice might still shine through, leading to a possible rebellion against Voldemort later on.
Well, in this fanfiction, perhaps Voldemort adopts Harry because he realizes Harry has some unique power that he wants to control. As Harry grows up, he starts to understand Voldemort's motives and tries to find a way to break free. He could also form unexpected alliances with some of Voldemort's followers who have a change of heart.
In this kind of fanfiction, one possible scenario is that Harry's whole view of the wizarding world would be warped. Voldemort might try to mold Harry into his own image. He could teach Harry dark magic instead of the traditional magic taught at Hogwarts. Harry might grow up with a completely different set of values and powers, which would surely change the whole dynamic of the fight against good and evil in the wizarding world.
Harry's character would likely be a mix of confusion and determination. He'd be confused by Voldemort's teachings which go against his natural inclination towards good. But his determination to find his true self would remain. He might develop a sort of duality, acting one way around Voldemort and his followers, but secretly being someone else.
Well, perhaps the Percy Jackson fan would introduce Harry to the world of Greek mythology. Harry might be trained in combat styles different from what he learned at Hogwarts, like using a celestial bronze sword. He could also be exposed to demigod powers and might start to see magic from a whole new perspective, with a blend of Greek magic and Hogwarts' magic.
Well, it could be that Klaus, with his complex and often dark nature, sees something special in Harry. Maybe he wants to use Harry's magic for his own purposes at first. But as time goes on, he starts to develop a real bond with Harry, like a father - son relationship. Harry, on the other hand, might be both intrigued and a bit scared of Klaus at the start. Then he grows to understand Klaus better and they face different challenges together, perhaps against other supernatural beings who are envious of Harry's power or threatened by Klaus's new protege.
Well, one possibility is that Harry's magical abilities would create a whole new dynamic in the Cullen family. Maybe he could use magic to protect them from other vampires or threats. He might also introduce the Cullens to the wizarding world, leading to some really interesting cultural exchanges between the two very different groups.