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.
In this type of fanfiction, the relationship between Hermione and the Death Eater could be very complex. Maybe it starts as a hostile one, but as the story progresses, they might find some common ground or mutual understanding. It could also be a story of redemption for the Death Eater through Hermione's influence.
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.
There's 'The Unlikely Bond'. Here, the Death Eater, say Draco (as in some fanfictions he has Death Eater - like tendencies), falls in love with Hermione when they are paired for a school project. It shows how love can cross the boundaries of their different beliefs. Also, 'Shadow of Love' is a great one. The Death Eater is secretly protecting Hermione from the other dark forces, all because of his unspoken love for her.
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.
No, it is not appropriate. 'Smut' implies sexual content which is not suitable for general audiences, especially when it involves characters from the Harry Potter series which has a large following of young fans. Fanfiction should focus on positive aspects like character development, new storylines within the magical world, rather than delving into inappropriate and often non - canon sexual scenarios.
One possible scenario in such a fanfiction could be that Sirius is somehow forced or tricked into becoming a Death Eater. Hermione might then try to rescue him from the dark side. Maybe she discovers some ancient magic that can reverse the dark mark's influence on him.
Another theme might be the power of knowledge. Hermione is known for her academic prowess. In fanfiction, this knowledge could be the key to either defeating the Death Eater or changing their views. For instance, she might use her knowledge of ancient magic to counter the dark magic of the Death Eater.
She might react with caution at first. Given that Death Eaters are known for their cruelty, Hermione would be smart to be on her guard. She would likely start by gathering information about the escaped Death Eater, like his known abilities and any possible weaknesses.
She could also try to reason with the Death Eater. Hermione is known for her intelligence and ability to think on her feet. She might try to appeal to any sense of humanity the Death Eater might have, reminding him of the consequences of following Voldemort's evil path.