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 villain in the fanfiction. Maybe a new, powerful vampire who has a vendetta against Bella or her friends.
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.
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.
A new villain in the story could be responsible. This villain could be out to make a name for themselves by taking down Harley.
Perhaps an unknown ice sorcerer. Since the Frozen world has magic, a new character who is jealous of Elsa's power could target Anna to get to Elsa. They might use their ice powers to create dangerous situations for Anna, like making the ice floor slippery and causing her to fall and get hurt.
It could be Vilgax. He's one of Ben's most powerful enemies. Vilgax is always looking for ways to defeat Ben, and he might come up with a new and devious plan to hurt him. Maybe he teams up with other villains to ambush Ben when he's least expecting it.
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.
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.
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.
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.