Well, it would be a much more peaceful Hogwarts. Harry could focus on his studies and normal wizarding life without the constant threat of Voldemort. There would be no need for the Order of the Phoenix, and the Ministry of Magic could focus on other matters like improving magical education or relations with the Muggle world.
In a fanfic where Voldemort is already dead, the story could take on a whole new direction. There could be new villains or challenges that emerge. Maybe there are remnants of Voldemort's followers who still cause trouble, but on a much smaller scale. Or perhaps the focus could be on exploring the wizarding world's history and magic more deeply. Harry could be involved in uncovering ancient spells or lost magical artifacts. Hermione would have more time to pursue her academic interests without the fear of Voldemort's return looming over them all, and Ron could just enjoy a more laid - back life at Hogwarts, maybe focusing on Quidditch and having normal teenage wizard adventures.
If Voldemort were already dead in the fanfic, it would change everything. For one, Snape's role would be very different. He wouldn't be a double agent. Harry might not have the same level of fame or the special status he had when he was the 'Chosen One' to defeat Voldemort. The relationships between characters would also shift. For example, Draco Malfoy might not be as antagonistic towards Harry as his family was closely associated with Voldemort's cause, but without that, he could be more open to a friendly relationship with Harry.
If Voldemort was already dead in the fanfic, the characters would develop in very interesting ways. For instance, Neville would not have to find his courage in the face of Voldemort. He could develop his skills in Herbology more freely and perhaps become a renowned expert in the field much earlier. Luna Lovegood could explore her unique brand of magic and beliefs without the overshadowing of the Dark Lord. The Weasley family would be more at ease, and Fred and George could focus on their joke shop business without the fear of Voldemort - influenced regulations or attacks.
It would be really strange. Maybe Harry would have a different kind of magic, something more in line with the Dark Arts. His personality might be more conflicted, since he has the blood of the most evil wizard in his veins.
It would be a very strange and dark fanfic. Harry is the hero who is supposed to defeat Voldemort, so making him Voldemort's consort completely flips the original story's dynamic.
A 'Harry Potter' fanfic about Voldemort and a cooking slave might start with the slave's capture or how they came to be in Voldemort's service. The slave would likely be treated very poorly, with Voldemort showing no mercy. The cooking aspect could be used to show the contrast between the normalcy of cooking (a homey, everyday activity) and the horror of being in Voldemort's presence. There could be other characters in the fanfic, like Death Eaters who interact with the slave in different ways, some might be more cruel, while others might have a bit of pity. And perhaps the slave could have some hidden power or knowledge that could eventually be used against Voldemort, leading to a potential escape or a change in the power dynamic in the story.
In such a fanfiction, it might be a very dark and twisted story. Harry could be forced to learn dark magic from Voldemort, which would completely change his character and moral compass. He might struggle between the light and the dark side more intensely than in the original story.
In such a fanfic, Harry might be tortured for information about the Order of the Phoenix. Voldemort could try to turn Harry to the dark side, using his powerful magic to break Harry's will.
Well, in a fanfic where Harry joins Voldemort, it could be a very different story. Harry could start to learn the dark arts from Voldemort, which would change his character completely. He might be given new powers or abilities that are dark in nature. This would also cause a lot of confusion among the wizarding community. People who once looked up to Harry would be disappointed and afraid. And there would be a new dynamic between the Death Eaters and Harry, with some perhaps being jealous of the attention he gets from Voldemort while others might try to befriend him for their own gain.
In a fanfic with this scenario, the story would take a dark and twisted path. Harry joining Voldemort would mean that the values he once held dear are now being tossed aside. Voldemort would start to manipulate Harry, perhaps using memories of his parents' death to make him more bitter. The Order of the Phoenix would have to reevaluate their strategies as Harry now knows a great deal about them. And as Harry gets more involved with Voldemort's plans, he might start to see the world in a more cynical way. His magic could also change, becoming darker and more unpredictable as he delves into the dark arts under Voldemort's tutelage. This would lead to a series of events where the line between good and evil becomes blurred for Harry and for the readers.
As of 2022, the endings of the Harry Potter movies are as follows: In the movie Harry Potter and the Deathly Hallows, Voldemort successfully destroyed all of Dumbledore's legacy, including his pure-blood bloodline and his position as Headmaster of Hogwarts. At the same time, he destroyed the evidence that Harry and his friends were searching for Voldemort and trapped them in Azkaban. In the movie Harry Potter and the Deathly Hallows: Part 2, Harry and his friends finally escaped from Azkaban's prison and went to Voldemort's castle. In the castle, they had a final duel with Voldemort. Although Harry eventually defeated Voldemort, they also realized that the possibility of Voldemort's resurrection was very high. So the Harry Potter movies ended with Voldemort successfully destroying all of Dumbledore's legacy and trapping Harry and his friends in Azkaban Prison. Although they eventually defeated Voldemort, they also realized that the possibility of Voldemort's resurrection was very high, which meant that the whole story would continue to unfold.
A 'Harry Potter writes to Lord Voldemort' fanfiction might show Harry at his most desperate. He could be trying to negotiate for the safety of his friends and the wizarding community. In the letter, Harry might remind Voldemort of their shared past, like how they are both orphans, in an attempt to create some sort of connection or empathy between them.