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.
Draco might be initially shocked. He's used to seeing Hermione as a strong adversary, so seeing her cry would be unexpected. He could just stand there, not knowing how to react at first.
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.
Hermione could become withdrawn.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.
Hermione might initially be furious. She is a strong - willed character, so being tied up against her will would surely make her angry. She would probably start using her wits right away, trying to figure out a way to free herself, whether it's through magic or by tricking Draco.
Well, Draco could be very conflicted. On one hand, he has his own pride and his Slytherin upbringing which might tell him to stay away. But if he has developed deeper feelings for Hermione in the fanfic, he might put aside their past differences. He could start by using his family's resources to find a cure or at least better treatments for her cancer. He may also become more protective of her, keeping her away from those who might be unkind about her illness.
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 initially shocked. After all, Draco is usually seen as this tough Slytherin. But then she could feel sympathy. For instance, she might offer him a handkerchief without saying much at first.
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.