It changes the whole direction. Instead of a typical hero's journey, it becomes a story of a fall from grace. His actions will be different, leading to new conflicts. For example, he might oppose his old friends, creating a rift in the group.
The 'harry becomes corrupted' concept completely alters the plot. Firstly, it changes the power dynamics. If Harry, who was a powerful force for good, now turns bad, it gives an advantage to the dark side. His corrupted state can lead to him making alliances with unexpected characters. This can introduce new plot twists. His actions will no longer be in line with the values of the wizarding world, which will cause a stir among the characters. His corruption might also be a slow process, which can be used to build suspense throughout the fanfic. The other characters will have to decide whether to try to save him or to stop him, which becomes a major plot point.
Another aspect is the friendships. Hermione and a female Harry might have a different kind of friendship. They could bond over more female - centric experiences, like dealing with the boys at Hogwarts in a different way. And Ron's relationship with a female Harry could also be different, perhaps more protective or having a different dynamic altogether, which would then ripple through the entire plot of the story.
It can completely change the direction of the plot. For instance, if Harry absorbs the Horcrux early on, he may have to face different challenges than in the original story. He might become a target for both sides, as the good side could be wary of his new, Horcrux - influenced state, and the bad side might see him as a threat to Voldemort's power.
Well, often in such a 'harry becomes corrupted slash fanfic', a common theme is the transformation of his personality. He may start to show more self - centeredness instead of his usual selfless nature. And power is also a big theme. His corruption could be tied to his pursuit of power in an unethical way. For example, he might be tempted by dark magic powers that are usually shunned in the wizarding world. And his relationship with his enemies might change too, maybe becoming more like them in some aspects.
It can greatly change the plot. If Harry has a different name, like Ethan, for example, Voldemort might not target him as easily. This could delay the start of the main conflict in the story. Or, it could cause the Order of Phoenix to be more cautious in approaching him as they may not be sure if he's the 'Chosen One' with this new identity.
It can change the direction of Harry's character development. Instead of following a more traditional path of family - building, he has to find new meaning in his life. This could lead to him becoming more involved in mentoring young wizards or taking on more dangerous missions that he might have avoided if he had a family to think about.
It can add an interesting dynamic. For instance, it can create a power imbalance that drives the conflict or resolution. If Harry is submissive, other characters might take advantage of him, leading to a plot where he has to overcome this exploitation.
The dragon's overeating might also be a sign of some underlying emotional issue in the fanfic. Maybe it's stressed or bored, and this overeating is a way for it to cope. This could then lead to a deeper exploration of the dragon's character and relationships. Other characters might try to figure out why the dragon is eating so much and in the process, they could discover things about themselves and their relationships with the dragon as well. It could be a catalyst for character growth and development within the fanfic.
It can make some people view the series as having a much darker potential. Since the original series has its dark moments but is generally more family - friendly, these tortured fanfics can show a side that might shock those used to the more positive view.
It can create a lot of drama. For instance, it can lead to a rift between Harry and Ginny's friends who might be on different sides. Some friends might side with Ginny, thinking she has valid reasons for the rejection, while others might support Harry and try to get them back together.
It can greatly affect the plot. For instance, if Harry is female, the way Voldemort views her could be different. He might underestimate her in some ways or be more intrigued by her. This could change the sequence of their confrontations. Also, if Hermione is male, his friendship with Ron and Harry could have new tensions. Maybe he'd be more competitive with Harry, which could lead to different sub - plots within the story.