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 due to some sort of chakra imbalance. Naruto often uses a large amount of chakra, and if something disrupts the normal flow of his chakra, like a new and untested jutsu he attempts, it might result in his body having a negative reaction such as a high fever.
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.
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 this fanfic, a possible cause for Naruto's heart attack could be a hidden genetic defect. Maybe it was passed down from his parents or some sort of unknown bloodline trait that suddenly manifested. It could also be that he was exposed to a strange and powerful chakra that his body couldn't handle and it affected his heart negatively, causing it to malfunction and leading to a heart attack.
It could be due to over - exertion during a difficult mission. Naruto often pushes himself to the limit, and this time it might have taken a toll on his body, resulting in a high fever.
It could also be that he ate some magical food that didn't agree with him. For example, he might have tried a new kind of magical sweet from Honeydukes that had a strange side effect on his digestive system. Another reason could be that he was under a minor curse. Some of the dark wizards or witches in the story might have cast a spell on him that caused his stomach to ache as a form of petty revenge or to distract him from something important.
In the fanfic, it might be due to a ninja technique gone wrong. For example, if he was trying a new jutsu that affected his internal chakra flow and it ended up giving him a tummy ache. This could be a really interesting plot point as it shows the risks of experimenting with new powers.
Well, it could be that he ate some bad ninja food. Maybe he ate a spoiled ration from a mission. You know, in the world of Boruto, they might not always have the freshest supplies on long missions.
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.
Yes, it is possible in fanfiction. In the Naruto universe, Susanoo is typically associated with the Uchiha clan. For Naruto to have Susanoo in fanfiction, one idea could be that through some kind of chakra - related experiment or perhaps a connection with an Uchiha's spirit. It could make for an extremely powerful Naruto. He might use Susanoo's strength combined with his own Sage Mode or Nine - Tails chakra, creating a whole new level of combat abilities.
It could be really interesting. Naruto is known for his strong will and determination. If he had Zangetsu, he would likely try to master it quickly. Since Zangetsu has a mind of its own in the Bleach series, there could be some fun interactions between Naruto and the sword spirit. He might even use Zangetsu to cut through some of the toughest jutsu barriers or opponents that he couldn't defeat with his normal techniques.