Perhaps Draco saves Hermione in a very public and unexpected way. This could lead to a huge scandal in the wizarding world. Lucius might be shamed and lose a lot of his influence among the Death Eaters. Draco, on the other hand, might find himself an outcast among his own family and former friends. Hermione, feeling indebted to Draco, might try to protect him from the backlash, which could further develop their relationship in an interesting way. It could also be that Draco's act of saving Hermione is part of a prophecy that neither of them knew about. This could add a layer of mystery and destiny to their story.
Well, it could be that Draco has fallen in love with Hermione secretly. So when he sees Lucius about to harm her, he can't help but step in. After saving her, he tries to hide his true feelings, but Hermione starts to notice little things about him that are different. She might be confused at first, but as she gets to know this new side of Draco, she begins to trust him more. Meanwhile, Lucius is furious with Draco and tries to punish him in some way, which adds more drama to the story.
Another plot twist could be that Lucius's act of saving Hermione causes a rift between Hermione and Ron that is hard to repair. Ron might misunderstand Hermione's connection with Lucius and think she is now on the 'dark side' so to speak. This could lead to a complex love triangle situation where Hermione has to prove her loyalty to her friends while also dealing with her gratitude towards Lucius.
One possible plot twist could be that the marriage law is part of a political ploy. Maybe the wizarding government wants to unite the pure - blood and Muggle - born factions through this law. Hermione, being the strong - willed character she is, initially resists but then realizes she can use this situation to advocate for better Muggle - born rights within the pure - blood society. Lucius, on the other hand, has his own motives, perhaps trying to regain some of his lost status in the wizarding world by being seen as more 'open - minded' through this marriage.
Draco might be motivated by jealousy. He could be jealous of Ron and Hermione's friendship or a possible romantic relationship between them. So he tries to harm Hermione out of spite.
The plot could start with Hermione being in a dangerous situation near water, like she might be attacked by a water - based dark creature while near a lake at Hogwarts. Draco, who might be nearby for some reason, overcomes his initial hesitations (due to their past enmity) and jumps in to save her. After that, they could start to see each other in a new light, leading to a slow - burn relationship as they deal with the aftermath of the incident and the reactions of their friends and the Hogwarts community.
Well, it changes Draco in many ways. Firstly, he realizes that there are things more important than loyalty to his family's dark cause. Saving Hermione makes him see the goodness in people like her. It could also make him more determined to change the reputation of his family. He may start to work secretly against the Death Eaters, using his knowledge of their plans from being part of the Malfoy family. His relationship with Hermione could also be a catalyst for his character growth, as she challenges him intellectually and morally, pushing him to become a better person.
One reason could be Snape's sense of justice. Despite his often - cold exterior, he might not tolerate Draco's bullying behavior towards Hermione.
Perhaps Draco and Lucius find Hermione after she's been attacked by some dark creatures. Lucius might be more interested in using her injury to his advantage in the wizarding politics. But Draco, who has always had a bit of a soft spot for Hermione's intelligence and bravery, secretly tries to nurse her back to health. As Hermione recovers, she manages to outwit Lucius and also makes Draco question his family's allegiance to the Dark Lord.
One possible plot twist could be that the tie - switching is part of a magical prank gone wrong. Maybe Hermione and Draco accidentally swap more than just their ties in a spell - mishap. This could lead to them experiencing each other's daily problems at Hogwarts. For example, Draco might have to deal with Hermione's heavy class schedule and the pressure from her friends to always be the top student, while Hermione has to face the Slytherin's snide remarks towards her as she now looks like one of them.
Often, a plot twist might involve Hermione uncovering a secret that Lucius has been hiding. This could be related to some dark magic he's involved in or a family secret. This discovery could then give Hermione some leverage over Lucius. Or perhaps there's a twist where other characters from the Harry Potter universe get involved. Like Harry and Ron coming to rescue Hermione, but she refuses to leave because she's in the middle of a complex plan to bring down Lucius from the inside.
In many such fanfictions, Sirius might use his magic skills. He could be quicker and more powerful than Lucius in a duel. Maybe he uses a powerful spell to stun Lucius and then whisks Draco away to safety.