Another possibility in the fanfiction is that Naruto caught a disease while on a mission in an unknown territory. He might have come into contact with a strange pathogen that his body is not used to, which then led to a fever.
It could be that he was exposed to some kind of a powerful jutsu's side - effect. Maybe an enemy used a jutsu that had a hidden impact on Naruto's health, leading to a fever. For example, a jutsu that disrupts the body's natural energy flow.
In the fanfiction, Naruto might have a fever due to overusing his chakra. When he pushes his body to its limits in intense battles or during extensive training, it could strain his body and cause a fever.
Maybe he was poisoned during a battle. The poison could be slowly affecting his body and causing a fever as his body tries to fight it off. In fanfiction, the poison could be something unique created by an enemy ninja with special properties.
It could also be that she came into contact with someone who was ill. In the close - knit community in Poldark, diseases can spread easily. If she was near a person with an infectious illness, she might have caught it and developed a fever as a result.
In such a fanfiction, Naruto might be really weak and vulnerable. His friends could be very worried about him. Sakura, as a medic - ninja, would probably be the first one to check on his condition and try to bring his fever down with her medical skills.
There are several possible causes. One is that it could be a hidden malignancy. Cancers like leukemia can present with just a fever in the early stages. Another cause might be a reaction to an environmental factor, such as long - term exposure to certain chemicals. Additionally, some genetic disorders can lead to abnormal immune responses that result in a fever of unknown origin. In some cases, a parasitic infection that is not typically screened for can be the culprit.
Well, it could be about Sonic's friends trying to take care of him while he has a fever. Maybe Tails uses his gadgets to monitor Sonic's condition and Knuckles brings some special herbs that are supposed to help with fevers in their world. And Amy could be fussing over Sonic, making him soup or something.
One possible cause could be over - exertion during a fight. Naruto is known for pushing himself to the limit. If he has been in a long and intense battle, it might put too much strain on his heart. Another cause could be some sort of poison or dark jutsu that specifically targets his heart function.
In fanfiction, it might be a result of a curse or some dark magic. For example, a villain could have cast a spell on him that weakened his heart both physically and emotionally.
Iruka - sensei could be an interesting option. He was Naruto's first teacher and has always had a soft spot for him. He would bring the warmth and comfort of a father figure. He might not have the advanced medical skills like Sakura, but he would stay by Naruto's side, tell him stories to keep his spirits up, and do whatever he can to help Naruto get better.
In the fanfiction, it could be related to her powers. Since her powers are a big part of who she is in the AOS universe. If she's just starting to understand and control them, it might be causing her subconscious to be in turmoil, thus resulting in nightmares. Also, her relationships within the team could be a factor. If there are conflicts or unspoken tensions with her colleagues, that could play out in her nightmares.
Naruto Sensei could be really weak and delirious from the fever. His students might be confused about how to take care of him at first. But then they would figure it out. For example, Naruto might keep mumbling about ramen in his feverish state, which could be a cute moment.