Another possibility is a jealous student. This student could be envious of Hermione's intelligence and Hagrid's popularity among the students. So, they use some sort of illegal magic to create disturbing events around Hermione and Hagrid. For instance, they might make Hagrid's hut collapse or make Hermione's books disappear in the middle of an important exam, all in an attempt to make them look bad and cause them distress.
It could be a rogue wizard who has a grudge against Hogwarts. He might be using dark magic to create disturbing situations for Hermione and Hagrid to deal with. For example, he could be making the magical creatures in Hagrid's care go wild or messing with Hermione's study time by causing strange noises and apparitions in the library.
A dark creature that has made its way into Hogwarts could be the antagonist. Maybe it's a Dementor - like being that spreads fear and despair, which disturbs Hermione and Hagrid. It could be feeding off the negative emotions of the students and causing the whole school to be in a state of unrest. Hermione and Hagrid would have to find a way to either drive it out or destroy it.
One possible plot could be that Hermione and Hagrid accidentally stumble upon a dark magic experiment in the Forbidden Forest that disturbs their normal routine. They then have to work together to contain the magic before it spreads and causes chaos in Hogwarts.
Perhaps an ancient evil force that has been trapped in the Sorting Hat for centuries and is trying to use Hermione as a means to break free. The force could start influencing Hermione's thoughts and actions in a negative way, and she has to fight against it with the help of her friends and the positive magic of Hogwarts.
A group of Death Eater sympathizers within the Ministry could be the main antagonists. They still hold onto the old pure - blood supremacist ideals and see Hermione, a Muggle - born witch, as a threat. So they fabricate evidence against her and send her to Azkaban to send a message to all Muggle - borns that they are not welcome in the new wizarding order they are trying to create.
One common theme is mentorship. Hagrid, being older and more experienced in the magical world, often acts as a mentor to Hermione. For example, he might teach her about the more secretive or dangerous aspects of magical creatures that she wouldn't learn in a classroom.
It's completely unacceptable. The 'Harry Potter' series has a certain set of values and character dynamics. Hermione and Hagrid have their own places and relationships within that world. Creating a 'lemon' fanfic with them not only violates the integrity of the story but also can be offensive to the fans who love the original, family - friendly nature of the series.
In some fanfics, Hagrid might help Hermione with her studies related to magical creatures. Since Hagrid has extensive knowledge about them, he could offer her special insights or take her on private excursions to study unique creatures.
It could be that Ron's own insecurities and pride are personified as an antagonist. His jealousy towards Hermione's achievements and friendships could be like a dark cloud over him. Severus has to save Hermione from this negative side of Ron. So in this case, Ron's inner demons are the antagonists that Severus must combat.
A dark wizard from the past whose secrets are being unearthed because of Hermione's exploration of the Chocolate Frog Card could be the main antagonist. Maybe the wizard was banished long ago and doesn't want his secrets revealed. He could start to influence events at Hogwarts through dark magic, trying to stop Hermione from learning more about him. For example, he could possess other students or create dangerous obstacles in Hermione's path.
One possible plot could be that 'Cage' is a magical artifact that Hagrid discovers in the Forbidden Forest. He shows it to Hermione, and they realize it has some sort of powerful magic. Maybe it's a cage that can hold dark creatures but is starting to malfunction, and Hermione and Hagrid have to figure out how to fix it before the creatures it's holding escape and cause chaos in Hogwarts.
Another possibility is an ancient evil that has been awakened. This entity might see Hermione as a threat because of her potential power. So it curses her to stop her from growing stronger. In this case, the antagonist would be very powerful and mysterious, and Hermione and her friends would have to do a lot of research and exploration to find a way to defeat it.