There are several. Some focus on Snape's early days as a Death Eater. For example, in one fanfic, it details how he was recruited, his initial thoughts on Voldemort's ideology, and how he gradually started to question it. It also shows how his relationships with his fellow Death Eaters were formed and evolved over time.
One common theme is Snape's internal conflict. Since he was a double agent, fanfictions often explore the turmoil he felt between his loyalty to Voldemort as a Death Eater and his real allegiance to Dumbledore. Another theme is his relationships with other Death Eaters, like Bellatrix or Lucius.
Sure. When searching for such fanfiction, it's important to read reviews if available. A well - written 'Death Eater Stalks Hermione' fanfic could add new dimensions to the Harry Potter universe. It might show Hermione using her intelligence in new ways to deal with this threat, perhaps by using her knowledge of magic in unexpected and creative ways to protect herself and others from the stalking Death Eater.
Snape could be very cautious in his interactions. He would be constantly aware of the power dynamics. He might flatter the more powerful Death Eaters subtly to avoid suspicion. For instance, he could compliment Bellatrix on her loyalty to the Dark Lord. At the same time, he might try to intimidate the weaker ones to show that he's not to be trifled with. He might use his knowledge of the Dark Arts to his advantage in these interactions, like casually mentioning a difficult spell he's mastered to gain some respect.
I'm not sure about a specific 'Bella is a Death Eater' fanfiction that stands out above all others. However, you can try searching on fanfiction - specific websites. Look for ones with high ratings and positive reviews. Usually, those are the ones that handle the concept well, whether it's the character development of Bella as a Death Eater or the overall plot within the Death Eater - centric world.
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.
He could be suspected by Voldemort. Since Voldemort is very paranoid, an injury at a meeting might make him think Snape is up to something or being careless in a way that could endanger their plans.
There's also the possibility that it was an accident. Fanfiction often plays with the idea of magical accidents. Maybe a spell misfired during a demonstration or a fight that broke out among the Death Eaters that Snape got caught in the middle of, and as a result, he got injured.
A possible plotline could be that Severus was framed as a Death Eater. He might be trying to clear his name throughout the fanfiction. Another idea is that he is part of a secret organization that is dedicated to taking down the Death Eaters from the inside, but they have to operate in secrecy so it appears he is one of them.
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.