In a fanfic with Hermione as Voldemort's spy, it's a very interesting concept. First of all, Hermione is known for her intelligence and loyalty in the original series. But if she's a spy, her intelligence could be used against the good guys. She could be using her knowledge of spells and magic to deceive her friends. The plot could involve her gradually realizing the error of her ways and trying to turn against Voldemort. Or perhaps she's so deep in the spy role that she becomes a real antagonist, causing chaos and destruction among the characters we love.
It makes her seem more powerful. Traditionally, Hermione is seen as the brains of the trio, but in this fanfiction, she's scarier, which implies a new level of power that goes beyond just being intelligent. It gives her an edge that we don't usually associate with her character.
It changes the story by adding a new layer of heroism to Snape. In the original, his heroism was more in the background. But here, he becomes Hermione's savior from Voldemort. This could also change Hermione's view of Snape completely.
Well, it could change a lot. For example, Hermione might have some internal conflict about her family connection to Voldemort. Maybe she would try to hide this fact from her friends. Also, Voldemort might have different plans regarding Hermione, instead of just seeing her as an enemy like in the original story.
One possible motive could be fear. Voldemort is extremely powerful and if he threatened Hermione or her family, she might feel compelled to spy for him. Another motive could be a thirst for knowledge. Voldemort might have promised her access to dark magic knowledge that she couldn't get anywhere else.
His reaction would likely be very different. At first, he might be angry that he didn't know this before. But then, he could start to see opportunities. He may think that if he can somehow control Harry as a Horcrux, he can gain more power. So, he might change his strategy from simply trying to murder Harry to trying to subdue him in a different way.
In a fanfic where Hermione is the heir of Slytherin, it would likely make her more of an outcast among her Gryffindor friends at first. They might not understand how she could be related to Slytherin, the house that has often been associated with the dark arts. However, it could also bring her closer to some Slytherin characters who would welcome her as their heir. This new status could give her access to secrets and knowledge that were previously unavailable. It might also force her to re - evaluate the history of Hogwarts and the rivalry between the houses, and perhaps find a way to bridge the gap between Gryffindor and Slytherin.
There are many ways this could happen in fanfic. One way is that Harry uses his connection with Voldemort's mind. Since Harry has a link to Voldemort's thoughts, he might be able to pick up on Voldemort's doubts about Snape. And then Harry starts to investigate Snape further. He might recall some strange actions of Snape in the past, like his ambiguous loyalty during certain battles or his secret meetings with some unknown figures. Combining all these, Harry eventually realizes that Snape is a spy.
Well, if Hermione was adopted by Voldemort in fanfiction, it would completely change the dynamic. First, Hermione's intelligence could be used in very different ways. She might be forced to use her knowledge to help Voldemort's dark plans, but she could also secretly try to undermine him from within. Second, her relationships with other characters would be altered. For example, her friendship with Harry and Ron would be put to the test. They would likely see her as a traitor at first, but later might realize she's playing a double - game. And finally, Voldemort himself might change. Having Hermione around could expose him to different ideas, though he'd probably resist them. It's a really interesting concept for a fanfiction.
Well, if Hermione was Voldemort's daughter, it would completely turn the story upside down. For one thing, her friendship with Harry and Ron would be in jeopardy. Harry would be very suspicious of her, considering he's Voldemort's archenemy. Also, the Hogwarts faculty might treat her differently. Dumbledore, who was always vigilant against Voldemort, would keep a very close eye on her. This could lead to Hermione feeling isolated and having to really prove her loyalty to the side of good.
He becomes more conflicted. Knowing he's Voldemort's son, he's constantly in turmoil about his true nature. His confidence might waver as he wonders if he's capable of the same evil as his father.