One possible reason could be the long - standing rivalry between Gryffindor and Slytherin. Hermione, being a Gryffindor, has always seen Draco as an adversary. So, in a fanfic situation where they are brought together in some way, her past experiences and prejudices might make her scared. For example, Draco has taunted her and her friends many times before.
It could also be that the fanfic has a new and unknown element in the relationship between Hermione and Draco. Maybe there is a prophecy or a strange magical bond that she doesn't understand. The uncertainty of what this new connection means for her future and her identity as a witch could be the source of her fear.
Perhaps in the fanfic, there is some sort of dark magic or a dangerous situation that involves Draco. Hermione, being a cautious and rule - following witch, might be scared of getting involved with something that goes against her principles or puts her in danger. If Draco is involved in some illegal or immoral magical activity, Hermione's fear could be a result of not wanting to be associated with it.
He could also be protective. Despite their differences, Draco might have some hidden feelings for Hermione. So, when he sees her scared, he might put aside their past enmity and try to comfort her or keep her safe from whatever is causing her fear. For instance, if there is a threat from another student or a magical creature, Draco could use his Slytherin cunning to protect her.
One possible reason could be fear. Maybe Hermione is afraid of how Draco will react. Given their history in the wizarding world, with their houses being rivals at Hogwarts and different beliefs, she might think he'll reject her or the baby. Another reason could be to protect the baby. There could be some threats or dangerous situations in the wizarding world that she believes Draco's knowledge of the pregnancy would put the baby at risk. For example, there could be dark forces that target the children of powerful witches and wizards, and she wants to keep the baby's existence a secret to safeguard it.
Voldemort or his remaining Death Eater followers are likely. Even if Voldemort is defeated in the original story, in fanfiction, there could be a resurgence or some secret followers still causing trouble. Another character could be Snape. In some interpretations, his motives are always a bit murky, and he could do something that scares Hermione. And of course, there could be new and original characters created by the fanfiction writer, like a powerful and evil witch or wizard from a far - off land who has a vendetta against Hermione.
One possibility is that it represents a shift in their relationship. Maybe Draco has always overlooked Hermione in a way, but seeing the scar makes him view her in a new light, as someone who has been through real challenges and is more complex than he initially thought.
It could be related to a specific event in the fanfic. For example, if she's going undercover for some mission, changing her hair color might be part of her disguise. Also, perhaps she's influenced by someone she admires and decides to copy their hair color.
Maybe it's because of their different outlooks on life in the wizarding world. Hermione is very much about following the rules and using magic for good and knowledge, while Draco has been more influenced by the power - hungry and sometimes underhanded ways of his family. This could lead to constant arguments and ultimately a break - up.
There could be several reasons. Draco might be facing some sort of blackmail. Someone could be forcing him to be with another person for some hidden motives. Also, his own pride could play a part. He may not want to admit that he's falling for Hermione, a Muggle - born in the eyes of some in the wizarding world. So, to prove to himself that he doesn't care about her as much as he thought, he cheats. Additionally, he could be influenced by the peer pressure within the Slytherin house, where some might not approve of his relationship with Hermione and push him towards someone else.
She could be defiant at first. Hermione is a strong - willed character, so she might immediately start trying to escape or use her magic against Draco. She could also try to reason with him, asking him why he's doing this and trying to appeal to his better nature.
One possible reason could be if Harry takes a big risk without consulting her first. In the wizarding world, their adventures are full of danger, and Hermione is often the cautious one. If Harry jumps into a situation like facing a powerful dark wizard alone without a proper plan, Hermione would likely blame him for being reckless.
One possible plot reason could be a misunderstanding. Maybe Draco thinks Hermione has some information that she's not sharing and he ties her up to force her to talk. In some fanfictions, it could be part of a game or a dare within the magical world they inhabit. Another reason might be that Draco is being influenced by some dark magic or a curse that makes him act out of character and tie Hermione up.