A great plot twist could be that the Death Eater she's betrothed to is actually a double agent himself. All along, Hermione thought she was the one with the upper hand in the undercover operation, but it turns out he's been playing a long - game too. This would completely change the power dynamic between them and add a whole new layer of complexity to their relationship.
Maybe the Death Eater has a long - lost family connection to Hermione. It could be revealed that he is related to her in some way that neither of them knew before the betrothal. This would force Hermione to re - evaluate her feelings towards him and the entire situation. It also adds an element of fate to the story, as if they were meant to be in each other's lives for reasons other than the betrothal.
Perhaps Hermione's transformation into a Death Eater is a result of a time - travel accident. She goes back in time, something goes wrong, and she ends up being influenced by the Death Eaters of that era. This would create a complex web of cause and effect in the fanfiction.
A possible plot twist could be that Hermione gets turned into a Death Eater against her will, and Draco has to help her break free from the dark magic controlling her. This would completely reverse their typical roles.
Well, it could be a time - travel fanfiction. The Death Eater might be from a different era, one where he hadn't fully committed to the dark side yet. Hermione gets betrothed to him in the past, and through her knowledge of the future, she tries to prevent him from becoming a full - fledged Death Eater. This would create a very interesting dynamic as she battles against the forces that are pulling him towards the dark side while also dealing with the social implications of being betrothed to someone with such a dark future.
One potential plot twist could be that Hermione's father was actually a double agent. So, while everyone thinks she's the daughter of a Death Eater, in reality, he was working for the good side all along. Another twist might be that Hermione discovers she has some special powers because of her heritage that can be used to defeat Voldemort in a unique way. For example, she could have an innate understanding of dark magic that helps her counter the Death Eaters' spells.
Another aspect could be an unexpected bond forming between Hermione and the Death Eater. As they are forced to spend time together, they might start to understand each other on a deeper level. This could lead to a moral dilemma for the Death Eater, especially if he starts to develop feelings for Hermione. He would then have to choose between his loyalty to the Death Eaters and his new - found connection with her.
One interesting plot twist could be that they are betrothed due to a magical contract made by their ancestors to end an old feud between the Gryffindors and Slytherins. Hermione at first resists but then discovers Draco has a kinder side she never knew. Another could be that in the middle of their betrothal, a dark wizard tries to use their union for his own evil purposes, forcing them to work together to stop him. And perhaps, after all the chaos, they realize they actually love each other in a way they never expected.
One common plot twist is that Hermione was actually a double agent all along. She pretends to be a Death Eater spy but is really gathering information for the Order of the Phoenix. This adds an element of mystery and excitement as the other characters in the story are initially unaware of her true motives.
One plot idea could be a werewolf Death Eater who is forced to work with Hermione under some strange circumstances. Maybe they are both on a mission to retrieve a powerful magical artifact, and along the way, the werewolf starts to question his loyalty to the Death Eaters as Hermione shows him the value of kindness and justice.
One idea could be that Draco and Hermione are forced to work together undercover among the Death Eaters. They start off distrusting each other but as they face various challenges within the Death Eater ranks, they begin to understand each other better. For example, they might have to find a way to stop a particularly heinous Death Eater plan while pretending to be on their side.
One idea could be Hermione discovers she has a long - lost pureblood heritage that has some ties to the Death Eaters. Maybe her family was involved in some secret Death Eater plot in the past, and she has to uncover the truth to clear her family name.