The relationship between Hermione and her friends would be shattered. Harry and Ron would be in shock and disbelief. This would also lead to a different path for Hogwarts. With Hermione on the side of the Death Eaters, she could potentially influence the school in a negative way, changing the educational system and the safety of the students. The overall tone of the wizarding world would become much darker as Hermione's character was often associated with hope and light in the original story.
Some in the wizarding world might see it as a chance for redemption for the Death Eater. If Hermione can reform him, it could be seen as a positive thing. But most would still be very cautious and watchful, fearing that it's all a ruse by the Death Eaters to cause more chaos.
The wizarding world would be in chaos. Harry has been seen as the 'Chosen One' to defeat Voldemort. If he becomes a Death Eater, the hope that the wizarding world has placed in him would be shattered. People would lose faith in Dumbledore's judgment for believing in Harry all this time. The Order of the Phoenix would be severely demoralized as they have been fighting for Harry's cause.
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.
Hermione's character could be developed by showing her internal struggle. If she has a pureblood connection to Death Eaters, she might question her own identity. For example, she could struggle with the dark side of her family history while still holding onto her values of justice and knowledge.
It could make her more empathetic towards the idea that not all Death Eaters might be completely evil. The fanfiction might show some grey areas in their characters.
The wizarding world would likely be shocked. Hermione has always been seen as a defender of the light and the rules. Helping a Death Eater would make many people question her motives and loyalty. Some might think she has turned to the dark side.
The most obvious change would be the relationship dynamics. Instead of the main focus being on Harry's battle against Voldemort, it would shift to Hermione's complex relationship with Voldemort. Her friends like Harry and Ron would be in a difficult situation, not knowing whether to trust Hermione or not.
In 'bella is a pureblood and death eater' fanfiction, the theme of identity is prevalent. As a pureblood in the Death Eater circle, she has to constantly reaffirm her identity. Is she just a tool of the Dark Lord? Or does she have her own motives? Also, the theme of secrecy and betrayal often comes up. She may have to keep secrets from her family or face betrayal from her fellow Death Eaters due to her pureblood status.
Betrayal might be a factor. If she felt betrayed by the wizarding community she was trying to protect, she could be pushed towards the Death Eaters. For example, if she was wrongly accused of a serious crime and the so - called good wizards turned their backs on her.
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.