A more complex plot could involve Hermione being transported back in time to a period when the Death Eaters were more prominent. There, she has to interact with a Death Eater who is different from the others, perhaps more morally ambiguous. They end up influencing each other's views on magic and the wizarding world. This kind of time - travel plot combined with the Hermione - Death Eater dynamic can lead to a very engaging and rare fanfiction.
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.
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 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.
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.
One possible plot idea could be Hermione using her intelligence to outwit the Death Eaters in a mind - game. For example, she might pretend to be on their side while secretly working against them to save her friends. Another could be a scenario where she has a strange connection or shared past with a particular Death Eater that she discovers during a dangerous encounter.
One interesting plot could be Hermione's struggle with identity in a world that has different expectations of a black witch. She might face unique forms of discrimination within Hogwarts and use her intelligence to fight against it. For example, she could form a club to promote equality among different races in the wizarding world.
One popular fanfiction in this theme might be 'The Darkest Path'. In it, the author creates a tense situation where Hermione is forced to deal with the Death Eaters' schemes in a very immersive way. Another could be 'Forced Alliance' which shows Hermione having to form an uneasy alliance with a Death Eater under duress.
One popular one might be 'Dark Affections'. In it, the complex relationship between the Death Eater and Hermione unfolds in a very intriguing way. It delves deep into the moral and emotional struggles of both characters. The author does a great job of showing how Hermione's intelligence and strong will interact with the Death Eater's dark nature.
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.
One idea could be a story where Death the Kid has to team up with a character from Soul Eater to face a new, powerful enemy that threatens the balance between the world of humans and the world of demons. They might start off not getting along due to their different personalities and ways of doing things, but as they face challenges together, they learn to respect each other and combine their strengths to defeat the foe.