Draco Malfoy could be a likely antagonist. He might be jealous of the friendship or whatever relationship is developing between Fred and Hermione and try to cause trouble for them. Another could be some of the more strict professors who don't approve of their unorthodox ways of doing things.
In this fanfiction, it's possible that an ancient magical creature that has been awakened in Hogwarts could be an antagonist. This creature might not like the presence of Fred and Hermione in certain parts of the castle and start causing chaos. Or perhaps there is a new dark wizard who has infiltrated Hogwarts, and he targets Fred and Hermione because they are known for their intelligence and bravery, and he wants to stop them from interfering with his evil schemes.
The pure - blood supremacists could be antagonists. They might not like the idea of Harry, a half - blood, inheriting Hogwarts and try to undermine his authority.
The Ministry of Magic itself could be an antagonist. If Fred and Hermione are running away because they've uncovered some sort of corruption or dark secret within the Ministry, the Ministry officials would want to stop them from spreading the truth.
Well, it's a wild fanfiction concept. Fanfic writers might play with the idea by having some sort of magical mix - up or a different relationship path for Hermione. Maybe there's a spell gone wrong that leads to this unexpected pregnancy. But it would surely be a huge departure from the original story's themes and relationships.
Often, it could be dark wizards or witches who are envious of Hermione's status as the heir. They might want to take over Hogwarts themselves or steal the power that comes with being the heir. For example, a powerful dark wizard who has been in hiding for years might emerge to challenge Hermione.
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.
Voldemort could still be an antagonist even if they are trying to change the future. His dark magic and his followers might oppose Harry and Hermione's attempts to rewrite history in a way that doesn't benefit them.
Well, perhaps in this fanfiction, Fred and Hermione could be paired up for a special assignment by a professor. They start off not getting along because of their different personalities, but as they work together, they realize they have more in common than they thought. For example, they both have a strong sense of loyalty, Fred to his family and Hermione to her friends. They could end up using their combined skills to save a part of Hogwarts from a magical threat.
One potential antagonist could be a rogue ninja who also has aerokinesis but uses it for evil. He might be jealous of Naruto's natural talent and try to undermine him at every turn. Another could be a powerful sorcerer from a far - off land who has come to the Naruto universe specifically to find someone with aerokinesis to either steal their power or use them as a tool. There could also be a group of anti - ninja who see Naruto's new power as a threat to their plans of overthrowing the ninja system and they try to eliminate him.
One way could be through a time - travel plot. Maybe Hermione travels back in time and ends up in a relationship with Fred instead of Ron, and then the pregnancy occurs. Another option is a magical accident where a spell affects their emotions and actions towards each other, leading to the situation.
Perhaps Orochimaru could still be an antagonist. In this fanfiction, he might be jealous of Naruto's new god - like gaming powers and try to steal them for his own experiments.