The Death Eaters would also have different character development. They might initially be suspicious of Harry, but as he proves his loyalty to Voldemort, they could start to accept him. Some might even see him as a potential leader in the future. Harry's development might also include changes in his magical abilities. Since he's learning from Voldemort, he could gain new and dark forms of magic. This would change his perception of himself and how others see him. His appearance might even change, becoming more gaunt or having a darker aura, which is a physical manifestation of his internal change.
Abraxas Malfoy could be developed to have a more sympathetic backstory. For example, he was pressured into certain actions by his family but secretly wanted a different path. Harry Potter could be developed in a way that shows his growth in understanding the gray areas of the wizarding world. By interacting with the idea of Abraxas Malfoy, he realizes that not all pure - bloods were simply evil. He could learn from Abraxas' story and use it to change his views on some of the long - standing prejudices in the wizarding community.
A female Harry Potter's character could be developed in a way that she challenges Lucius Malfoy's traditional pure - blood beliefs in a more diplomatic way. Instead of just fighting against him, she tries to understand his point of view and then show him the flaws in it. Lucius, on the other hand, could be developed to have a redemption arc that is triggered by his interactions with this different version of Harry Potter. He might start to question his loyalty to Voldemort and his own prejudices.
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.
In fanfiction, Harry might be more worldly. Since he gets more exposure to Viktor and Durmstrang, he could pick up on different magical traditions faster. For example, he might start using some Bulgarian hexes in his duels. Viktor, on the other hand, could be shown to be more open - minded. In the books, he was a bit reserved. In fanfiction, he could be more eager to learn about Hogwarts' ways and make more friends there.
Some characters might develop new skills. For instance, Hermione could learn a type of magic from another universe that makes her even more powerful. This would change her role in the story and how others interact with her.
Well, in fanfiction, Severus' character can be developed to show his softer side towards Lily earlier on. In the books, we mainly see his tough exterior and his actions as a double agent. But in fanfiction, we might see him expressing his love for Lily in more open and desperate ways. As for Lily, she could be developed in a way that she is more empathetic towards Severus' situation. In the books, she seemed to cut him off quite harshly, but in fanfiction, she might try to understand his reasons for getting involved with the Death Eaters and still hold some hope for their relationship.
For Bellatrix, instead of just being a crazed Death Eater, she could be shown as having a more complex relationship with the lemon - like it reminds her of a childhood memory that softens her a bit. Narcissa could be developed to be more independent and less influenced by her family's dark ways because of her connection to the lemon. And Harry Potter could be more empathetic towards them because of the lemon's influence on their personalities.
The relationship between them in fanfiction also affects their portrayals. If the fanfiction focuses on a timeline where Dumbledore and Voldemort were once friends or colleagues, their characters will be different from a story where they were always bitter enemies. Dumbledore might show more regret or a sense of failure if he couldn't prevent Voldemort from turning evil in such a scenario, and Voldemort might have a different level of respect or hatred for Dumbledore depending on their past interactions.
In fanfiction, their characters might be given more in - depth backstories. For example, we could learn more about their family life outside of Hogwarts. Maybe Parvati has a special relationship with an elderly relative who is a powerful witch, which wasn't mentioned in the books.
In the fanfiction, Snape might be developed with more of a sense of humor. For example, in the original series, he is very dour, but in the fanfiction, his interactions with Harry in the context of a risky business situation could bring out a side of him that cracks jokes or uses sarcasm in a more light - hearted way. This would be a big departure from his usually serious self in the books.