a death eater decides to help hermione fanfiction

One reason could be that the Death Eater has a family member who was saved by Hermione or her friends. So, out of gratitude, he decides to help her.

The development might also involve the Death Eater introducing Hermione to some secrets of the Death Eater organization in a bid to undermine it from within. This would be a very risky move. Hermione, being the clever witch she is, would have to be very cautious in dealing with this new - found ally. She would need to constantly assess whether his help is genuine or part of a bigger trap. Their relationship would be full of tension and mutual suspicion at the start, but gradually they could learn to trust each other more as they work towards a common goal, like bringing down Voldemort's regime.

It could also be that Hermione is on a mission to gather information. By helping the Death Eater, she hopes to gain insider knowledge about the Death Eater's group or their plans. This would be a strategic move on her part, using the situation to her advantage in the fight against the dark forces.

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.

Well, in such a fanfiction, perhaps the Death Eater could initially be reluctant to help Hermione. But if there's some common goal, like stopping a greater evil in the wizarding world that might affect both the good and the Death Eaters' side, they could form an uneasy alliance. For example, a powerful dark magic artifact is about to be misused by a new dark wizard and Hermione realizes she needs the inside knowledge of the Death Eaters to stop it.

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.

Another idea could be that she is somehow brainwashed. There could be a dark spell or a powerful magical object that alters her perception and makes her believe in the Death Eater ideology. In this scenario, her friends would have to find a way to break the spell and bring her back to her true self.

One possible aspect of this fanfiction could be Hermione's encounter with an unexpected Death Eater. Maybe she stumbles upon one during a mission or while exploring a hidden area. This encounter could lead to a series of thrilling events, like a battle of wits or a dangerous duel.