On the other hand, Draco might misinterpret Hermione's tears as a sign of weakness and use it to his advantage in the fanfic. He could taunt her further, which would add more drama and conflict to the story.
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.
One possible reason could be a sudden outburst of pent - up emotions. Maybe Hermione has been bottling up her feelings for a long time, and in the presence of Draco (in the context of the fanfic), something triggers her to break down. It could be a situation related to the ongoing conflict between Gryffindor and Slytherin in the Hogwarts setting, and Draco represents all the stress and frustration she has with that divide.
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.
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.
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Hermione could become withdrawn.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.
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.
In many fanfics, Draco's reaction turns into a sense of protectiveness. He feels a need to shield Harry from any further harm, whether it's from the people who abused him in the past or from the judgment of others. For example, in some stories, he'll stand up to those who make snide remarks about Harry's past, using his Slytherin cunning to put them in their place. He also tries to be a source of comfort for Harry, which is a big change from their initially antagonistic relationship.
Hermione's parents would probably be very concerned at first. They are Muggles and know little about the wizarding world's prejudices. They might worry that Draco will not treat Hermione well because of his family's past views. As for Draco's family, his father might be disdainful initially. However, his mother might be more open - minded, especially if she sees how much Draco loves Hermione.
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.