Harry could become more relaxed. After all the battles and traumas of his youth, as an adult he might be more at peace. He could be less impulsive and more calculating. Dudley, having matured, might lose his bullying nature completely. He could be more empathetic, especially after experiencing some hardships in his own life that made him realize how his actions affected others.
As an adult, Harry might develop a more diplomatic personality. He has dealt with so many different types of people in the wizarding world that he could be great at handling difficult situations. Dudley could become more open - minded. Growing up in a somewhat sheltered Muggle world, as he gets older, he might be more willing to accept the existence of magic and the different world Harry comes from. This would change his perspective on a lot of things and make him more inclusive.
Harry could become more confident and self - assured as an adult. He has been through so much in his youth that he would have a strong sense of self. Dudley might become less of a bully. Maybe he has a family of his own and has learned to be more kind and patient, influenced by his own family life.
Harry might become more open and less guarded. Since he now has a brother in Dudley, he might feel more at home in the Muggle world. Dudley, on the other hand, could become less of a bully. The knowledge that he has a wizard for a brother could make him more humble and empathetic.
It could completely transform their relationship. If they have a positive reunion, they might become friends. They could start to support each other in different ways. Harry could use his magic skills to help Dudley out in small ways, like fixing something around his house without Dudley knowing it was magic. Dudley, in return, could offer Harry some insights into the Muggle world that Harry might not be fully aware of.
Well, Harry and Dudley's relationship would change drastically. Harry, by adopting Dudley's child, is taking on a huge responsibility. Dudley might initially be in denial about the whole situation, but as time passes, he realizes that Harry is providing a better life for his offspring. This could lead to a thaw in their long - standing animosity. Harry might start to view Dudley as someone who has made mistakes but is also trying to do right by his child in his own way. And Dudley could start to view Harry as a real family member, someone he can rely on.
In some fanfictions, they might become grudging friends. As adults, they could start to understand each other's past traumas better. Dudley, having grown up and away from his parents' influence, might realize how unfairly he treated Harry as a child. Harry, on the other hand, might see Dudley's attempts at change and begin to trust him more.
Well, if Harry and Dudley became friends, it would drastically change the whole dynamic of the early Harry Potter story. For one, Harry might not have felt so alone at the Dursleys' place. Dudley could have protected Harry from Vernon's wrath. Also, they could have shared secrets about the wizarding world with Dudley being a Muggle. This new friendship might even have led to Dudley developing an understanding and acceptance of the magical world much earlier, and perhaps he could have been an ally to Harry in the fight against Voldemort, instead of a bully.
Well, it changes their relationship in that they become closer. Dudley's overprotective nature means he starts to see Harry as someone precious to him. This could lead to them sharing secrets. Harry might tell Dudley more about the wizarding world, and Dudley could confide in Harry about his insecurities. They might even team up against common enemies, like those who look down on both of them for different reasons. Overall, it makes their relationship more complex and interesting.
Dudley could start to view Harry in a more empathetic way. Fanfiction might show Harry dealing with emotional struggles that Dudley can relate to, like feeling lonely or misunderstood. Through these stories, Dudley might see that Harry is not so different from himself in some ways, which could change his view from one of annoyance or envy to one of understanding.
In these fanfictions, Harry may develop a more diplomatic side to his personality. Since Draco is from Slytherin and has a different way of thinking, Harry has to learn to negotiate and find middle ground. For Draco, his friendship with Harry can make him more empathetic. He might start to care about the well - being of others outside of his Slytherin clique, like the Gryffindors and other Hogwarts students, which is a big change from his initial self - centered attitude.
Harry might become more relaxed around Draco. He's used to being on guard against Draco's taunts, but as friends, he lets his guard down. He may start to show his more humorous side and not be so serious all the time. For Draco, he could become less arrogant. He realizes that Harry isn't just the 'Chosen One' to be hated but a real person with his own struggles. He might start to be more empathetic, which is a big change from his usual self - centered attitude.