One interesting plot twist could be that Lucius tries to use Hermione as a spy within Dumbledore's Army. He might think that he can manipulate her into getting information for the Death Eaters. But Hermione, being as clever as she is, turns the tables on him and feeds him false information. Another twist could be that Hermione discovers a long - lost family secret that explains how she and Lucius are related and that this secret has the power to either redeem Lucius or completely destroy the Malfoy family name.
A great plot twist could be when Hermione, despite being Lucius' sister, is chosen as the one to take down Voldemort. Lucius then has to choose between his loyalty to Voldemort and his sister. This would create a huge internal conflict for him. Also, what if Hermione's Muggle - born status was actually a cover - up by the Malfoy family for some greater purpose? This would rewrite a lot of the backstory and create many new storylines and mysteries to be explored.
One interesting plot twist could be that Naruto actually has a hidden power that is the key to Hagoromo's own power development. Maybe Hagoromo has been struggling with something in his power growth, and Naruto's presence unlocks it. Another could be that Naruto is from the future, and his knowledge of future events causes a huge shift in the way things are supposed to happen in Hagoromo's time.
Perhaps a plot twist could be that the time - travel device they use was actually created by an ancient and forgotten wizard who had a hidden agenda. When Hermione and Lucius travel back, they discover that this wizard was trying to use them to change history for his own gain. They then have to race against time (literally) to stop this wizard from achieving his goal while also trying to return to their own time. This would add an extra layer of mystery and danger to their time - traveling escapade.
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.
Well, a really interesting plot twist could be Hermione's role in the Slytherin house. She could become a leader, using her intelligence to reform the house's more negative aspects. Or, she might be caught in the middle of a power struggle between different Slytherin factions. Also, her interactions with the Slytherin pure - blood families could be full of drama. Maybe she discovers a family secret that could change the whole wizarding world.
One cool plot twist is when Hermione discovers that Edward has a hidden power that is related to her magic. Maybe he can absorb and use some of her magic energy, which leads to a whole new set of challenges and adventures as they try to understand and control this new aspect of their connection.
In some fanfictions, the plot twist is that Hermione's magic has a different effect in Middle - earth than it does in the Harry Potter world. For instance, her spells might accidentally cause a rift between different races in Middle - earth, and she has to find a way to fix it while also dealing with the main quest of the dwarves to reclaim Erebor. It adds a whole new layer of complexity to the story.
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.
A really interesting plot twist could be that Snape was under a spell all along that made him seem so cold and distant, and Hermione discovers it. This changes the whole dynamic between them. Another twist could be that Hermione is actually related to someone from Snape's past in a way that they never expected, which brings them closer.
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.
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.