In some fanfictions, the writer likes to explore extreme and dark scenarios. So it could be that Jiraiya has his own personal demons and issues. He might have a moral conflict within himself and somehow comes to the conclusion that killing Naruto is the solution. For example, if Jiraiya believes that Naruto's power is too dangerous and uncontrollable, and no other options are available to stop him from causing chaos, he may take the drastic step of killing him.
Perhaps in this fanfiction, Jiraiya discovers that Naruto is going to be the cause of a major catastrophe in the future. He might have seen a prophecy or some sort of sign that convinces him Naruto has to die to prevent this. It could also be that Jiraiya has been misled by false information about Naruto, which makes him think that Naruto has become an evil force that needs to be eliminated.
There could be a 'naruto kills jiraiya fanfiction'. It could be based on a time - travel scenario. For example, if Naruto from the future travels back in time and somehow his actions cause a chain of events that lead to Jiraiya's death. Or perhaps there's a dark, alternate universe where Naruto's values are twisted and he sees Jiraiya as an obstacle to his new, malevolent goals and thus kills him.
It would be quite a shock to the Naruto fandom. Jiraiya is a beloved character and Naruto is the protagonist. For some fans, it would be a very dark and disturbing concept. It might make some fans angry as it goes against the typical relationship and character development in the original series.
One possible reason could be that Naruto feels he has learned all he can from Jiraiya at that point. Maybe he has reached a level in his training where he believes he needs new experiences and challenges that Jiraiya can no longer provide.
One possible reason could be mind control. Some dark power might take over Naruto's mind and force him to turn on Jiraiya without his own will.
In the Naruto universe, bringing someone back from the dead is extremely difficult. While there are some jutsu like the Edo Tensei that can reanimate the dead, it has its limitations and is often considered dark magic. For Naruto to revive Jiraiya, he would need to find a way around the natural laws of life and death. However, in fanfiction, anything is possible as it allows for creative interpretations and bending of the established rules.
One possible reason could be that Naruto feels he has learned all he can from Jiraiya at that point. Maybe he wants to explore his own path independently and test his skills without Jiraiya's constant guidance.
The impact would be significant. Since Naruto has such a large and passionate fandom, this fanfiction would be like a bomb. Some fans would stop reading fanfictions altogether if they find this concept too disturbing. Others might start creating counter - fanfictions where they try to rewrite the scenario to something more in line with the original spirit of the series. It could also lead to a decrease in the popularity of the overall fanfiction community related to Naruto if this kind of extreme and negative content becomes more common.
Jiraiya might comfort Naruto by sharing his own experiences. He could tell Naruto about the times he faced difficulties and how he overcame them. For example, he might talk about his training with the toads and how he grew stronger through perseverance.
Perhaps Jiraiya has some personal issues or inner conflicts. He might be dealing with his own past traumas or demons that prevent him from taking on the role of Naruto's trainer. For example, he could be haunted by the failures in his previous relationships or battles, and he feels unfit to train Naruto until he sorts out his own problems.
One possible motive could be that Kakuza has committed some heinous crimes against the Hidden Leaf Village. Maybe he has been involved in secret attacks on the village or has been plotting something really bad that would endanger the lives of many villagers. Naruto, being the protector of the village, would then take it upon himself to stop Kakuza by any means necessary, which unfortunately might end up in killing him.