A twin brother might change the plot significantly. For example, if he was bolder than Harry in some ways, he could be the one to first confront Draco Malfoy and start a feud that affects the relationships between the houses differently. Also, he could have a different relationship with Dumbledore. Maybe he doesn't trust Dumbledore as much as Harry does, which would lead to different strategies in the battle against the dark forces.
The twin could change the plot by being more interested in academic magic than Harry. This might lead to him uncovering secrets in the library that Harry misses, which could be crucial in the fight against Voldemort.
In fanfiction, Harry's twin brother could change the plot in multiple ways. Let's say he had a natural talent for divination. He might foresee events more clearly than Harry. This could lead to them preparing for battles or challenges in a different way. He could also have a different view on the use of dark magic. If he was more open to exploring it (not in an evil way, but for self - defense), it would create a conflict with Harry and other characters. And his presence could also change the way other characters interact with the Potter family, as there are now two Potters to consider instead of one.
In this fanfiction concept, the story would be turned on its head. The whole mystery around Harry's parents and his connection to Snape would be reimagined. Their shared heritage as twins could lead to new magical abilities that they discover together. The Hogwarts houses might even treat them differently. For instance, Snape being a Slytherin and Harry being a Gryffindor in the original, but as twins, there could be a whole new dynamic within the houses. And the final battle with Voldemort could be fought in a completely different way with their combined strength and new - found relationship.
Well, it would completely disrupt the original dynamic. Harry's relationship with his friends and the wizarding world was centered around his own journey. If he was abandoned for his brother, his brother might become the 'chosen one' figure in this new scenario. This would mean that Harry might grow up feeling resentful or neglected, and his magical abilities could develop in a very different way, perhaps in secret. It could also lead to a different set of alliances and enmities within the wizarding world.
Well, if Hermione had a twin sister in fanfiction, it could change the story in many ways. For example, there could be more help for Harry and Ron. The twin sister might have different skills or knowledge that could assist them in their adventures. Maybe she's better at potions or has a special connection with certain magical creatures. It would also add more family drama and relationships to explore. Hermione's relationship with her sister could be a mix of love, rivalry, or both. This new character could also interact differently with the other students at Hogwarts, like having her own group of friends or enemies.
Well, if Hermione was James' twin sister in a fanfiction, it would completely change the dynamics. For one, Hermione's intelligence and magical ability would be part of the Potter family from the start. The Marauders might have had an even more powerful member in their group. And Hermione could have influenced James' actions towards Snape in a different way, perhaps lessening the animosity between them. It could also mean that Hermione would have a different backstory, growing up in the Potter household instead of with Muggles.
Well, if Naruto was Anko's twin brother in a fanfiction, it could completely change the relationships in the story. For example, Naruto would have a different family dynamic. He might not be as alone as he was originally, having Anko as a twin. This could also affect his training. Maybe Anko would have pushed him to be more like her in some ways, like in combat styles. And his relationship with other characters such as Sasuke and Sakura would also be different. Anko might be more protective of Naruto and be more involved in his rivalries.
The plot could involve the two of them having different magical abilities despite being twins. Harry might inherit more of his mother's protection magic while James could have some other unique power. They could also have different relationships with Sirius, with Sirius perhaps being more protective of both of them. And when they go to Hogwarts, they could have different reactions to the Sorting Hat. James might be sorted into Gryffindor right away, but Harry could be a Hat - stall between Gryffindor and another house, which could create an interesting story arc about his identity and loyalties.
The plot could center around the twin's discovery that there is a dark secret society within Durmstrang. They are initially reluctant to get involved but are forced to when they realize the society's plans could endanger not only Durmstrang but also the entire wizarding world. The twin then uses their knowledge from Hogwarts and their new - found skills at Durmstrang to try and stop the society, facing many dangerous obstacles and betrayals in the process.
If Naruto were Sakura's twin brother, the story would be very different. Naruto would have someone in his family from the start, which would have affected his personality. He might not be as eager to seek attention and approval as he was in the original story. In terms of their ninja training, they could have learned from each other. Sakura might have taught Naruto some of her book smarts when it comes to ninjutsu theory, and Naruto could have shown Sakura some of his more unorthodox but effective combat techniques. Their relationship with Kakashi as their sensei would also change, as Kakashi would have to deal with the unique bond between the two siblings.
It would completely transform the story. Hermione being Lily's twin would mean that the Marauders might have interacted with Hermione as well. Sirius and Remus might have seen her as an additional person to protect. And Hermione's presence could have potentially led to different outcomes in the events leading up to James and Lily's death. She might have been able to come up with a different plan to hide from Voldemort, using her vast knowledge of magic.
In the fanfiction, Auryn could hold a prophecy that relates to both universes. This would bring characters from Harry Potter and Naruto together to either prevent or fulfill the prophecy. The search for the meaning of the prophecy within Auryn could drive the plot, as characters have to cooperate and overcome challenges from both their worlds.