Well, it could be due to Draco's growth as a character. In the fanfic, he might have fallen in love with someone who makes him see the good in Harry. Love has a way of changing people's perspectives. It could also be that he finally understands the true meaning of friendship and realizes that his enmity with Harry was pointless. Also, he may have witnessed Harry's selfless acts towards others, which makes him feel ashamed of his own behavior and prompts him to apologize.
Harry might be initially skeptical. After all, Draco has been his tormentor for a long time. He may think it's a trick or some sort of ploy. But if Draco is sincere, Harry could gradually accept the apology. He is a forgiving person at heart.
One possible reason could be a misunderstanding during a mission. Maybe Rhodey made a decision that put Tony in danger without realizing it at first, and later realized his mistake. For example, if Rhodey called for backup in a situation where it attracted more enemies towards Tony. Another reason might be something related to their personal relationship outside of the hero stuff. Perhaps Rhodey said something unkind about Tony's new technology, not knowing how much effort Tony had put into it.
One reason could be that James finally realizes the extent of his bullying. In the original story, James often harassed Snape. In fanfiction, he might come to understand how much pain he caused Snape and feel genuine remorse. Another reason could be that he discovers new information about Snape that makes him see Snape in a different light. For example, he might find out about Snape's love for Lily and how his actions towards Snape affected Lily as well.
Draco may use Crucio on Harry due to his own insecurities. He might feel overshadowed by Harry all the time. His family's expectations to uphold their pure - blood superiority could also play a role. He could think that by using Crucio on Harry, he can assert his power and show that he's not to be trifled with. It could also be that he's caught up in the moment of a heated argument or rivalry and loses his temper completely.
One possible reason could be for a power play. Draco, being from a Slytherin family, might want to show his dominance over Harry, who is seen as a hero in the wizarding world. By tying him up, he could be trying to intimidate Harry or gain some sort of advantage in their ongoing rivalry.
One possible scenario could be that Harry realizes he misjudged Draco all along. Maybe he discovers that Draco was acting out of fear or family pressure rather than pure malice. For example, Draco might have been forced to take on certain tasks by his Death Eater father, and Harry finally understands this and apologizes for always being so hostile towards him.
It often changes for the better. After Harry apologizes, Draco might be initially skeptical. But as they start to interact more, they could become friends or at least develop a mutual respect. For instance, they might start sharing their experiences during the war, which helps them understand each other better.
One possible reason could be their long - standing rivalry. Draco has been taught to dislike Harry from a young age due to their family differences. His pure - blood supremacist upbringing might make him reject Harry as a mate because Harry is seen as a 'Mudblood - lover' in the eyes of Draco's family and their circle. Another reason could be fear. Draco might be afraid of what the wizarding society would think if he accepted Harry as his mate. The wizarding world has its own set of norms and expectations, and a relationship between them would be highly unconventional and likely face a lot of opposition.
One possible reason could be that in the original 'Harry Potter' lore, Draco and Harry are from rival houses and have a history of animosity. So in fanfiction, Draco might reject Harry based on this pre - existing enmity. For example, Draco's pure - blood supremacist views might clash with Harry's more inclusive attitude.
One possible reason could be that in the fanfic, his parents might be depicted as having made some big mistakes in the past that directly affected Harry in a negative way. For example, they could have made a deal with a dark force that put Harry in danger later on.