Perhaps it's a mysterious figure in the fanfiction world. This unknown character could have some ulterior motives against Jacob and find ways to hurt him, like setting traps for him.
In some fanfictions, Jacob could get hurt while exploring an unknown area. There could be some sort of hidden danger, like a trap set by an enemy. Or perhaps he gets hurt in a natural disaster that occurs while he's in his wolf form and unable to fully protect himself. For example, a sudden landslide or a forest fire.
Bella's actions in the fanfiction might be another cause. Maybe she accidentally says or does something that undermines Jacob's self - esteem. Like if she makes a comment about his werewolf nature in a negative way, it could wound him deeply as it's an important part of who he is.
I'm not sure if there is a specific 'Jacob gets Renesmee pregnant' fanfiction. Fanfiction can cover a vast range of ideas, but this is a rather controversial and unusual plot. It might exist in some corners of the fanfiction world, but it also goes against some of the original concepts in the source material. You would need to search through various fanfiction platforms like Archive of Our Own or FanFiction.net to find out for sure.
There might be some extremely niche fanfiction out there with this concept, but it goes against the established lore of the 'Twilight' universe in many ways. Vampires in the 'Twilight' world are undead and have different biological functions compared to humans, and werewolves also have their own unique biology. So while fanfiction can be creative, this would be a very out - of - the - box and perhaps not very common plot.
Physical hurt might come from a powerful magic spell. Let's say an evil sorcerer casts a spell that drains Yami's energy and causes him pain. His struggle to overcome this and regain his strength could be a central part of the fanfiction.
Well, in a fanfiction plot, Nicole could be hurt while trying to protect her partner. For example, if there's a bomb threat in a building where they are. Nicole would shield her partner from the blast, resulting in her getting seriously hurt with burns and fractures. Or perhaps she gets into a car accident while rushing to a crime scene because of a mechanical failure in her vehicle.
One possible plotline could be that Tohru gets physically hurt during an accident while helping out at the Sohma house. Maybe she's climbing a ladder to fix something on the roof and slips, resulting in a sprained ankle or a cut. Another could be that she gets emotionally hurt when she overhears some of the Sohma family members saying unkind things about her, not realizing she can hear them. It could make her question her place in their lives.
Yuki would likely be very concerned. He has a soft spot for Tohru and would probably rush to her side, trying to find a way to help. He might even blame himself if he thinks he could have prevented it. Kyo, on the other hand, would initially be angry, but that's just his way of showing worry. He would be more hands - on in getting her the help she needs.