There could be a new dark wizard or witch emerging. This character could be jealous of Harry and Hermione's influence and see the baby as a way to get to them. They might try to harm the baby or turn it against Harry and Hermione, creating a lot of conflict and danger in the story.
In this fanfiction, the plot could start with Harry and Hermione realizing that they want to start a family together in a non - traditional way. They find a baby who has some special powers or a mysterious background. As they adopt the baby, they have to figure out how to raise it while also juggling their own lives as important figures in the wizarding world. They may need to seek help from their friends like Ron and Ginny to create a stable and loving environment for the baby.
Voldemort's remaining followers could be antagonists. They might see the baby as a new threat or a potential weapon. They could try to kidnap the baby to use its power for their own dark purposes.
One possible antagonist could be a dark wizard who wants the baby for its own dark purposes. Maybe the baby has a unique power that the dark wizard wants to harness. Also, there could be some jealous wizards or witches in the community who are envious of the Golden Trio's fame and don't want to see them succeed in this new family venture. They might spread rumors or try to create problems for the Trio and the baby.
The Ministry of Magic itself could be an antagonist. If they don't approve of Hermione's adoption due to her age or some bureaucratic reasons, they could try to take the baby away. They might think she's not fit to raise a child, which would create a lot of conflict in the story.
There could also be new dark wizards or witches who envy the power and fame that Harry and Hermione have. They might see the child as a way to get to Harry and Hermione, or they might simply want to prove themselves by challenging the family. For example, a dark wizard who has developed a new and dangerous form of dark magic and wants to test it on the child.
Often, it could be Death Eaters. They are the main villains in the Harry Potter series, so it makes sense for them to be antagonists in fanfiction where Harry and Hermione need to escape.
It could be a group of dark wizards who have escaped from Azkaban and formed a new dark alliance. They might be seeking revenge on Harry and Hermione for their role in defeating Voldemort.
Often, the goblins can be antagonists. If they have their own motives that conflict with Harry and Hermione's, like protecting a dark secret in the vaults or trying to take advantage of the situation for their own gain. Another possible antagonist could be a Death Eater who has infiltrated Gringotts to either steal something important or to ambush Harry and Hermione.
Well, perhaps in the fanfiction, Harry and Hermione find a child who has special needs in terms of magic. For example, the child has an uncontrollable magical power that scares other families away. But Harry and Hermione see the potential in the child. They start to work together, with Hermione using her vast knowledge of magic and Harry using his own experiences, to help the child learn to control their power. As they do this, they form a very close family unit.
In this fanfic, the social workers who are overly strict or have some biases could be antagonists. If they don't approve of Cheryl's lifestyle or think she has some flaws that make her an unfit adoptive mother, they could create a lot of obstacles for her in the adoption process. This would add drama to the story as Cheryl tries to prove herself worthy of adopting the baby girl.