The Death Eaters or their sympathizers can also be antagonists. Since Hermione is a prominent figure in the fight against Voldemort, they would see her as a threat and try to harm or capture her. This could involve elaborate plots to kidnap her and use her knowledge against the Order of the Phoenix.
In some cases, even some of the Hogwarts teachers who might be secretly working for the dark side or who have a grudge against Hermione could be antagonists. They could give her unfair punishments or try to sabotage her academic progress, which would add to her victimized state in the fanfiction.
Draco Malfoy is often an antagonist in such fanfictions. His family's beliefs in pure - blood supremacy could lead him to target Hermione, who is a Muggle - born witch. He might use his influence and his Slytherin friends to make her life difficult.
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.
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.
Some pure - blood supremacists could also be antagonists. They may see Harry and Hermione, especially if Hermione is an heir as a Muggle - born, as a threat to their idea of a pure - blood - only wizarding society. They would do whatever it takes to stop them from rising to power and using the founders' legacy to promote equality and change in the wizarding world.
Voldemort or his Death Eaters could be antagonists. They might see the pregnancy as a way to manipulate or harm Harry and Hermione. For example, they could try to use the unborn child as a hostage or a weapon against them.
It could be the Death Eaters. They might not want Harry and Hermione to succeed in the ritual as it could be a threat to their dark plans. Or maybe some other dark wizards who are envious of the power that the ritual might bestow on Harry and Hermione.
In Kidnaped Izuku Fanfiction, likely antagonists could be rival villains who see Izuku as a threat to their plans. For example, those who want to stop him from becoming a great hero. It could also be villains who are after his unique quirk. Maybe they want to study it or use it for their own evil purposes. Another possibility is that it could be a group with a vendetta against the hero school he attends, and they target Izuku to send a message.
The Akatsuki could also be antagonists in an Iruka kidnapped fanfiction. They might believe that Iruka has some information about the jinchuriki, especially since he is close to Naruto. Or there could be a new, made - up antagonist in the fanfiction, like a powerful dark wizard who has set his sights on Iruka for some unknown but sinister reason. This new antagonist could add a fresh and unique element to the story.
It could be the traditional villains from the original story, like the Titans or some powerful monsters. They might torture Percy to get information or just to cause chaos.
Another likely antagonist could be the government or some secret agency. They might see Danny as a threat because of his powers. In an angry fanfiction, they could be constantly trying to capture or study him, which would fuel Danny's anger. And Danny would have to fight against them to protect himself and his loved ones.
The Akatsuki could be likely antagonists. They are always interested in powerful ninja like Naruto. They might use some forbidden jutsu to control Naruto to further their goals of collecting the tailed beasts. Another possibility is Orochimaru. He is always looking for ways to gain power and Naruto's power would be very appealing. He could try to control Naruto to use him in his experiments or to fight his enemies for him.