One interesting concept could be the idea of a different Sorting Hat system. Maybe it sorts students based on different qualities or has a new set of houses altogether. Another could be a world where magic has different rules, like spells having unforeseen side effects that change the whole plot. For example, a simple levitation spell might make an object disappear instead.
It expands it by changing character fates. For example, if Neville becomes the chosen one instead of Harry. This simple change can lead to a whole new set of adventures and challenges. The entire story then revolves around Neville's journey.
Well, without having read the 'book of altered reality fanfic', it's hard to say exactly. However, it might be a story that plays with the concept of reality in an interesting way. It could be that different dimensions or parallel universes are involved, where the rules of reality are different in each one. The fanfic could be centered around a group of characters who are somehow transported between these altered realities. They might have to face different challenges in each reality, like different forms of danger or different moral dilemmas. This would make for an exciting and thought - provoking story.
Hermione Granger is often still very popular in these fanfictions. Even with an altered destiny, her intelligence and determination make her a central figure. She might be the one to figure out the implications of the changed destinies and come up with plans to deal with the new situations.
One interesting plotline could be where Harry is sorted into Slytherin instead of Gryffindor. This would completely change his relationships within the school. He might have to deal with different prejudices and form alliances with students he would have otherwise been at odds with in the original story.
Draco Malfoy often becomes a popular character in these fanfictions. In altered destinies, he might be shown in a more sympathetic light. For example, if his family is not as deeply involved with the Dark side early on, he could form friendships with characters like Harry. His internal struggles between the expectations of his family and his own moral compass can be explored more deeply.
One interesting concept could be how a character's altered magical core changes their spellcasting abilities. For example, if a character's core is infused with a different type of magic, they might be able to perform spells in a unique way that others can't. Another concept could be the origin of the alteration. Was it a result of a dark curse, or perhaps an experiment gone wrong? It could also lead to new relationships and power dynamics within the wizarding world as characters with altered cores might be seen as either threats or valuable assets.
Harry Potter himself is often a popular character in such fanfiction. His already - powerful magical core being altered can lead to all sorts of interesting storylines. Hermione Granger is also a favorite. Fans like to explore how her brilliant mind would deal with an altered core, whether it enhances her intelligence - related magic or gives her new challenges. Draco Malfoy is another one. Altering his core can create a whole new dynamic for his character, from his relationship with his family to his standing in the wizarding world.
One interesting plot could be that Harry is sorted into Slytherin instead of Gryffindor. This would completely change his relationships and how others perceive him. His friendships might form with different characters, like Draco Malfoy becoming a more positive influence on him rather than an antagonist.
Since I haven't read the 'book of altered reality fanfic', I can't say for sure who the main characters are. However, it's common in such stories for there to be a protagonist who is the one most affected by the altered reality. There might also be some sort of guide or mentor character who helps the protagonist understand what's going on. And perhaps there are antagonists who either caused the alteration of reality or are trying to take advantage of the chaos it has created.