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.
Another possibility is that Draco uses Hermione's fear to his advantage at first. He might try to manipulate the situation to get what he wants, like getting Hermione to do his homework or something similar. But as he sees the real distress in her eyes, he has a change of heart and decides to help her in a more sincere way.
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.
Hermione could become withdrawn. She might isolate herself from her friends for a while, spending her time in the library trying to make sense of it all. She might also feel a sense of betrayal, especially if they had some sort of understanding or relationship developing.
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.
Snape would probably be very stern with Draco. He might give him a severe scolding and deduct points from Slytherin. Snape is a strict teacher and he won't tolerate such behavior from his own house students.
Hermione could also try to reason with Draco. She'll probably start a conversation, trying to understand his motives for capturing her. She might appeal to his better nature if she believes he has one, or try to make him see the error of his ways by using her logical arguments.
She might be heartbroken at first. Hermione is someone who invests deeply in her relationships. She would likely retreat into her studies as a way to cope, burying herself in books to try and forget the pain.
Hermione could also be more understanding in some fanfictions. If she senses that there's something deeper behind Draco's actions, she might try to calm the situation down. She could ask him why he did it instead of immediately retaliating. Maybe she sees a glimmer of vulnerability in his eyes and decides to approach the situation in a more empathetic way. This could then lead to a conversation that changes their relationship for the better.
She might get angry and stand up for herself. Hermione is known for her strong will, so she could lash out at Draco verbally, using her intelligence to put him in his place.
Hermione might be initially very hurt and angry. She's a proud and strong character. She could cut Draco off completely and refuse to have any communication with him. When Draco shows regret, she may be skeptical at first. After all, he has broken her trust. But deep down, she might still have some feelings for him, so she could be in a state of internal conflict.
Hermione might initially be shocked and afraid, but she would quickly gather her wits. She would assess Draco, trying to figure out if there was any way to sway him to her side. Given her ability to see the good in people, she might try to appeal to any sense of morality Draco has left, all while secretly planning her escape or a way to undermine Voldemort's plan of using her as a pawn against the good side.