Sasuke would also be concerned, believe it or not. Despite their complex relationship, they are comrades and friends deep down. He might not show it outwardly as much as others, but he would be worried. And of course, Kakashi. As Naruto's teacher, he has a responsibility towards him. He would be using his wisdom to figure out a way to get Naruto back on his feet.
Definitely his friends from Team 7. Sakura, as a medic - ninja, would be extremely worried about Naruto's condition. She would be constantly checking his vitals and trying different medical techniques to make him better. And Naruto's other friends in the village like Choji and Shikamaru would also be concerned. They might come up with plans to keep Naruto's spirits high while he's sick.
His teammates, Sasuke and Sakura, would surely be involved. Sasuke, although he may not show it as much, still cares about Naruto. He would keep an eye on Naruto's condition, and if there was any sign of danger, he would be ready to protect him. Sakura would be more hands - on with the medical care, checking his temperature, giving him medicine, and making sure he rests properly.
His closest friends like Kagami would probably be very concerned. They have a strong bond on and off the court.
Maybe a rogue ninja group that wants to sell Naruto to the highest bidder. They see him as a valuable asset due to his strength and status in Konoha.
Sasuke would likely be very concerned. Even though he often has a cold exterior, his connection with Sakura is deep. He would probably visit her in the hospital secretly, not wanting to show too much emotion but still being there for her. He might bring her a special herbal remedy that he found during his travels.
One possible plot development could be that his friends rally around him. For example, Sakura might use her medical skills to try and figure out what's wrong. Another could be that Naruto's illness is somehow related to a new enemy or an old foe's hidden jutsu. It might also lead to Naruto having to rely on others more than he's used to, which could be a big character - growth moment for him.
Sasuke could be one of the people to help. Despite their past differences, Sasuke has a deep connection with Naruto. He might be able to understand Naruto's situation and offer his protection and support.
Sasuke could be a possible cause. If Sasuke were to go back on his word about protecting the village or if he were to harm their friends again, Naruto would be pissed. Their relationship is complex, and Sasuke's actions often have a strong impact on Naruto.
A rogue ninja from a rival village could be responsible. They might see Naruto as a threat and use their fire - based attacks to harm him. For instance, a ninja from the Hidden Mist Village who has a grudge against Konoha and targets Naruto specifically.
The entire village of Konoha could be highly affected. Naruto, with his second chance, could bring about positive changes in the village much faster. For the younger generation like Shikamaru, Naruto's new approach might inspire them in different ways. And for the older generation, they might be forced to re - evaluate their views on Naruto and the future of the village if he starts making radical changes early on.
Well, Naruto for sure. His friends from Team 7 are highly likely to be in it. But also, characters like Tsunade. As the Hokage and a great medical ninja, she could be consulted if Naruto's illness is really serious. Jiraiya might also make an appearance in Naruto's sick day fanfiction, perhaps reminiscing about his own times when he was sick as a young ninja.