One reason Draco as a Death Eater is alluring in fanfiction is the 'bad boy' image. It adds an edge to his character. Writers can use this to create more exciting and edgy storylines.
In fanfiction, Draco Malfoy as a Death Eater often presents a complex character. Some fanfics might explore his internal struggle between his loyalty to Voldemort and his own sense of right and wrong. He's a character that's full of contradictions in this context.
Well, it could be that Draco is forced to follow the Death Eater path while Hermione is fighting against them. But then, they might get thrown into some situations together, like being trapped in a place. Draco realizes that Hermione is not just a Mudblood in the sense that he was taught, and they start to form an unlikely bond. Their relationship could be full of tension, with Hermione constantly trying to convert Draco or at least make him see the wrong in what he's doing, and Draco struggling between his loyalty to his family's Death Eater ideals and his growing feelings for Hermione.
Bellatrix Lestrange is also a likely candidate. Her encounter with Hermione would be extremely intense. Given her loyalty to Voldemort and her rather unhinged nature, she would likely pose a serious threat to Hermione, but Hermione might also find a way to use Bellatrix's madness against her.
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.
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.
Bellatrix Lestrange's younger brother or some other minor Death Eater character could be used. This would allow for the creation of a new character with his own motives and backstory. He could be betrothed to Hermione as part of a larger plot by Voldemort to gain control over Hermione's knowledge and magic. This would put Hermione in a very difficult position as she would be tied to a very dark and dangerous family.
There's also a possibility that it could be a minor Death Eater that we don't know much about from the original series. The author of the fanfiction could create a new character who was a Death Eater but is now having doubts. Hermione could be the one to find this person and start their journey of change. This would give the author a lot of creative freedom to develop the character's backstory and their relationship with Hermione.
In Draco Malfoy family fanfiction, the relationship between Draco and his mother, Narcissa, can be really fascinating. Some stories might show Narcissa as a more protective and loving mother than we saw in the original books. For example, she could be secretly helping Draco make better choices away from the Dark Arts, which would change the whole family's path.
One great fanfiction where Draco Malfoy is a healer is 'Healing the Past'. In this story, Draco uses his skills to help those affected by the after - effects of the war. His character development is really interesting as he overcomes his past prejudices. Another one could be 'The Healer Malfoy', which focuses on his journey in the healing field, dealing with difficult patients and also his relationship with his former Hogwarts classmates.
One great fanfiction about Draco Malfoy as Headboy is 'The Headboy's Duty' on FanFiction.net. It shows Draco taking on the role with a new sense of responsibility. He has to deal with the challenges of Hogwarts in a more mature way, and it also explores his relationships with other students in a really interesting way.