Perhaps it could be a new character. A mysterious wizard who comes into Hermione's life, and they fall in love and have a child. This would add an element of newness and mystery to the fanfiction, as the readers would get to learn about this new character and his relationship with Hermione.
Another possibility is Harry Potter himself. This would be a very different take on their relationship. In some fanfiction, the strong bond between Hermione and Harry could be taken to a new level. Maybe in a situation where they are the last hope for the wizarding world, they conceive a child in secret to carry on some special magic or power that could save the wizarding community.
Another possibility is that the father could be a completely new character created just for the fanfiction. This new character could be a mysterious wizard who had a short - lived encounter with Hermione and then disappeared, leaving her to deal with the pregnancy on her own.
It could be Ron. Since they have a relationship in the original story, it's a very likely option. Their relationship could be further developed as they face the new chapter of becoming parents together.
It could be Ron Weasley. In many post - war fanfictions, Ron and Hermione get married and have children. Ron would be a great father, teaching the kid about wizarding traditions and Quidditch, while Hermione focuses on academics.
It could be Sasuke. Their relationship has always been complex in the original Naruto story. In the fanfiction, their relationship might have developed into a romantic one, leading to the birth of the child. The child would then inherit traits from both of them, perhaps Sasuke's cool-headedness and Fem Naruto's determination.
It could be someone completely new, an original character created for the fanfiction. Maybe a mysterious wizard who had a brief encounter with Ginny.
The adopted child could be a muggle - born with a great potential for magic. Maybe their parents were killed by dark wizards who were against muggles in the wizarding world. Harry and Hermione, having both experienced prejudice, would be determined to give this child a chance.
Annabeth could be the mother. Since she and Percy have a strong relationship in the original series, it's very likely that in a fanfiction they would have a child together. Their combined intelligence and Percy's powers would make for an interesting genetic combination for their child.
It could be Edward. Since they had a deep connection in the original story, it would make sense for him to be the father in the fanfiction.
Ron could be the father. Given their relationship in the original series, it would be a natural choice. They could have gotten married and had a son. Ron's laid - back nature might contrast with Hermione's more serious side when it comes to parenting their son.