A possible storyline could be that there's a prophecy about their union. It's a prophecy that could either bring great peace or great destruction to the wizarding world. Harry and the daughter then have to figure out how to navigate their relationship while also dealing with the expectations and fears of the prophecy.
The storyline could start with Harry encountering the daughter by chance. Maybe she's been in hiding all these years. He initially feels conflicted because of who her father was. But as he gets to know her, he realizes she's not like Voldemort at all.
It could be a story where the daughter is on a journey of redemption for her father's sins. Harry, being the symbol of good, decides to help her. Along the way, they develop feelings for each other. Their relationship could then be a central point in a story about forgiveness and second chances in the wizarding world, which would be very different from the typical good - vs - evil story we usually see in the Harry Potter universe.
In a fanfiction where Hermione is Tom Riddle's daughter, the storyline would be turned upside down. The prophecy about Harry and Voldemort might need to be re - evaluated as Hermione's connection to Voldemort could potentially change the balance of power. Her relationships with other characters would be complex. For example, Dumbledore might have had a different plan all along if he knew about Hermione's true parentage. The Death Eaters could also try to recruit her, seeing her as a way to get closer to Voldemort. This would create a whole new set of conflicts and challenges for Hermione, Harry, and Ron, and would lead the story in a completely different direction from the original.
Well, one possibility is that it would create a huge conflict within the wizarding world. Harry is seen as a hero and Tom Riddle (Voldemort) is the ultimate villain. His daughter would be a very controversial figure. Harry might face a lot of opposition from his friends and the wizarding community at large.
In such a fanfiction, Hermione's magical abilities could potentially be enhanced or different. Since Tom Riddle was a very powerful wizard, his genes might have passed on some unique magical traits to Hermione. This could make her an even more formidable force in the wizarding world. It would also change the way she approaches magic. Instead of relying solely on books and study, she might have an inborn understanding of some dark magic, which she would have to struggle to keep in check. Her relationship with Dumbledore would also be complex. Dumbledore would be both cautious and intrigued by her connection to Riddle.
It would be very strange. Maybe it would involve some sort of time - travel or alternate reality magic. For example, Harry could be sent back in time and through some magic accident, end up being in a situation where he is Tom Riddle's mother. The story would have to completely rewrite the established relationships and histories in the 'Harry Potter' world.
At first, it might be rocky. Tom would be suspicious of Harry's intentions. But as Harry shows him genuine care, Tom would start to open up. Eventually, they could become like family, with Tom looking up to Harry as a role model.
One plot idea could be Fem Harry growing up in the wizarding world with the secret of her parentage. She might start to notice strange similarities between herself and Tom Riddle's dark magic tendencies, but struggle against them. Another could be her discovery of her heritage leading to a conflict within the wizarding community, as some fear she will follow in her father's dark footsteps, while others believe she can break free from that legacy.
Her relationship with Dumbledore would be extremely complex. Dumbledore, knowing her parentage, would be both watchful and perhaps a bit more guarded around her. He would try to guide her away from the dark path but also might not fully trust her at first. With Ron and Hermione, they might initially be shocked and a bit hesitant. However, their loyalty to her as a friend could eventually overcome their doubts, but there would always be a bit of unease, especially when it comes to using dark magic.
Family and heritage play a big role. She has to deal with the fact that her father is one of the most feared wizards in history. There's often a theme of secrecy as well. She might have to keep her true identity a secret from her friends. Also, power is a theme. As Tom Riddle was powerful, she may inherit some of that power and has to decide how to use it, for good or evil.
Hermione would probably be very cautious at first. She would be worried about the potential danger that Tom Riddle could pose, even as a child. But she might also see it as an opportunity to study the roots of dark magic and how to prevent someone from turning to the dark side.
It could be a very complex relationship. Harry might be constantly on guard at first, but gradually start to see the good in Tom. Tom, on the other hand, could be using Harry for his own ends initially but then develop real feelings of friendship. They might study magic together, share secrets about their unique magical abilities.