In fanfiction, when Naruto gets injured by Pain, it could also trigger some new powers or abilities within Naruto. Maybe the injury acts as a catalyst for him to tap into a deeper level of the Nine - Tails' chakra. His injury might also make the other villages more aware of the threat that Pain poses. They could decide to form alliances with Konoha in order to deal with the Akatsuki as a whole. This would change the political landscape in the Naruto world.
Another scenario could be in a mission gone wrong. The fanfiction might depict a mission where Naruto and his team are caught off - guard by an ambush. There could be a large number of well - coordinated enemies, and Naruto might end up being the main target, getting severely injured as he tries to fight them off and protect his team.
The fanfic 'Naruto's Trial of Pain' is quite good. In it, Naruto is injured during a fight against a dark shinobi who has mastered a forbidden jutsu. The way the author describes Naruto's pain and his determination to keep fighting despite his injuries is really engaging. It shows his growth as a character and how he won't give up even when his body is on the verge of collapse.
Often, his friends like Sasuke, Sakura, and Kakashi might come to his aid. Sakura, being a medical ninja, would likely be the first to start treating his injuries. Sasuke could use his Sharingan to help in some way, perhaps to find the root of the injury or fend off any threats while Naruto is injured. Kakashi, with his experience, would also offer strategic advice on how to deal with the situation.
One possible plot development could be Naruto's friends rallying around him. They might seek out medical help, like Sakura using her skills to stabilize him at first. Then, they could start planning revenge against Pain. Another could be Naruto having some sort of vision during his injury, perhaps about his parents or a new power he could unlock to defeat Pain in the future. And, his sensei, Kakashi, could take on a more protective role over him as he recovers.
In some fanfictions, Naruto's recovery could be a long and arduous journey. He might have to go through intense physical and mental training while recovering. The author could also introduce some kind of ancient and forgotten medical knowledge that is used to treat his severe injuries. His recovery might also be tied to some prophecy or hidden power within him that is awakened due to the near - death experience.
Sasuke is very likely to be involved. Given their complex relationship, Sasuke could be the one who finds Naruto severely injured and has to make a choice between helping him or leaving him. Another character could be Sakura. As a medic - ninja, she would be the one to try and heal Naruto's severe injuries. Kakashi too might be involved, either as a mentor figure who tries to figure out what happened to Naruto or as someone who has to step in to protect Naruto from further harm while he is injured.
John was playing football when suddenly, he collided with another player. He felt a sharp pain in his leg and knew he was injured. His teammates rushed to his side, their faces filled with concern. The coach quickly called for the medical team. As John lay on the ground, he thought about how this might affect his future in the sport. But he also knew he had a great support system around him.
A plot could revolve around the power vacuum left by Naruto. The Leaf Village is in disarray, and other villages start to make moves against it. Pain might realize that killing Naruto wasn't really what he wanted in the long run, as it led to more instability. Or maybe a character who was in the background in the original story steps up to try and fill Naruto's shoes. They struggle to gain the respect and power that Naruto had, while also dealing with the grief of his loss.
In a fanfic where Naruto gets killed by Pain, it's a dark turn of events. The story would then likely focus on how the remaining characters cope. For example, Kakashi might feel a great sense of guilt for not being able to protect Naruto. Hinata would be heartbroken. Moreover, the Nine - Tails would be left without a host, which could also lead to all sorts of problems. The ninja world would lose its most prominent symbol of perseverance and friendship, and it would be a very different world from the one we know in the original Naruto story.