Perhaps one of the rival tribes or kingdoms sees T Challa as a threat and sends an assassin to hurt him. They might think that by injuring him, they can gain an advantage in the power struggle among different regions.
It could be a new villain who has emerged. This villain might have a personal vendetta against T Challa and specifically target him to cause harm.
Another possibility is a jealous student at Hogwarts. There are always students who might be envious of Hermione's academic achievements. They could set up a prank or a trap that goes wrong and ends up hurting her. For example, a student who is tired of Hermione always getting the top grades in Potions might tamper with her cauldron during a class experiment, resulting in an explosion that hurts her.
It could be a rival assassin. They might see Kassandra as a threat to their own reputation or contracts.
It could be a new, inexperienced doctor. Maybe they make a mistake during a surgery that Meredith is involved in, accidentally causing her harm. For example, they might misread a vital sign or use the wrong instrument.
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.
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 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.