In some cases, it could be herself. Maybe she pushed herself too hard in her work or training, and her body or mind couldn't take it anymore. This self - inflicted harm could be a key part of the fanfiction's plot, as she then has to deal with the consequences and learn from her over - zealousness.
Another possibility is that she gets hurt emotionally. Maybe a relationship in the fanfiction turns sour. A betrayal by a close friend or a lover could be considered as a form of 'getting hurt'. This could then lead to her making some different choices in the story and growing as a character from the pain she experiences.
A new villain in the story could be responsible. This villain could be out to make a name for themselves by taking down Harley.
It could be a villain in the fanfiction. Maybe a new, powerful vampire who has a vendetta against Bella or her friends.
In the fanfiction, it might be someone from his own team. Maybe there's a new member who is insecure and feels that Kuroko is getting too much attention. So, in a fit of jealousy, this person does something that causes Kuroko to get hurt, like tampering with his equipment.
It could be an enemy from the underworld. Maybe a powerful demon or a vengeful spirit that has a grudge against her. They might use their dark powers to harm her, like sending a bolt of dark energy her way.
Maybe it's a jealous acquaintance. If Kagami is really good at something, like she's a star in a particular activity, someone who is jealous of her success might set up a situation where she gets hurt. For instance, they could tamper with her equipment in a way that causes her to have an accident.
Another character who might be responsible is a jealous rival. This person could be envious of Elena's popularity or her relationship with someone important. So, they set a trap that causes her to get hurt.
Sometimes, it could be due to her own actions. Lydia might be overconfident and take risks that she shouldn't. For instance, she could try to perform a very difficult and dangerous magic spell without proper training, and it backfires, causing her to get hurt.
It could be a rival from another house. For example, a jealous Slytherin who wants to take Ginny out of the Quidditch game. They might use some underhanded tactics to make her broom malfunction and cause her to get hurt.
One common plotline could be that Felicity gets physically injured during some sort of conflict or accident. Maybe she's caught in the crossfire of a battle or a building collapse.