Maybe in the fanfic, Naruto could be afraid of losing his friends. For example, he might have a nightmare about his friends being killed in battle, which makes him constantly worried and afraid during his daily life.
Another possibility is that Naruto is afraid of failing to protect the village. The Hidden Leaf Village has always been his top priority to protect. If there are new threats that seem overwhelming, like a powerful new enemy or a mysterious plague that could destroy the village, his fear of not being able to safeguard it could be the focus of the fanfic.
One possible reason could be that they had a past traumatic experience related to explosions. Maybe they witnessed an explosion that caused harm to their loved ones or themselves. Another reason might be that explosions in the 'Naruto' world are often associated with powerful and dangerous jutsus or attacks, and they are simply afraid of the destruction and chaos that explosions can bring.
One possible plotline could be that they are in a village or a world where there is a sudden increase in the use of explosive jutsus or weapons. Naruto, Kiba and Issei have to face their fear as they are constantly under the threat of these explosions. Maybe they start off by trying to avoid areas where explosions are likely to occur. For example, they might stay away from battlefields or places where ninja experiments with explosive substances are taking place. As the story progresses, they could be forced into situations where they have to confront their fear directly, like when their friends or loved ones are in danger in an explosion - ridden area. This would be a great opportunity for character development as they learn to overcome their fear for the sake of others.
One great 'afraid of fear fanfic' could be 'The Fear Within'. It explores how the main character overcomes their fear by facing it head - on. Another might be 'Facing the Fearful Darkness' which delves into the psychological aspects of being afraid of fear itself.
One possible storyline could be Naruto being possessed by a Devilman - like entity. His friends then have to find a way to free him while dealing with the new, more dangerous Naruto. Another could be Naruto willingly accepting Devilman - like powers to defeat a greater threat, but then struggling to control them.
In some fanfics, Naruto might be depicted with PTSD (Post - Traumatic Stress Disorder). Given his rough childhood, the loss of his parents and the isolation he faced in the village could potentially lead to such an issue. Also, he could be shown to have self - doubt issues, constantly questioning his worth as a ninja despite his achievements because of all the years of being looked down upon.
One possible storyline could be that Naruto is kidnapped by a rogue ninja group who wants to use his power for their own evil deeds. They might try to force him to reveal the secrets of his special jutsu. Another could be that he is kidnapped by a mysterious organization that believes he is the key to a long - lost prophecy. They hold him captive while they try to figure out how to use him to fulfill the prophecy. A third storyline could be that Naruto is kidnapped by a group of enemy ninjas from another village who see him as a threat to their plans for domination.
One scenario might be related to a failed mission. Maybe Naruto is sent on a top - secret mission that is much more dangerous than anyone anticipated. He could be betrayed by someone he trusts during the mission, leading to his death. Or perhaps there are some unforeseen circumstances, like a strange and deadly curse that gets unleashed during the mission which he succumbs to.
I'm not a person to be afraid in a Naruto fanfic, but generally, characters might be afraid of a 'big bad wolf' - like figure if it represents a great threat. In Naruto fanfic, it could be a new, powerful and malevolent villain that shares some characteristics of a big bad wolf, such as being predatory and dangerous. But it really depends on the specific plot and how the author writes it.
It could be an old enemy who has come back with new and more terrifying powers. For instance, Orochimaru might return with some kind of jutsu that can directly target Naruto's mind and create unfathomable fears in him.
One possible mutation could be a chakra - related one. For instance, his normal chakra could mutate into a more powerful and different - colored chakra, like purple chakra that gives him the ability to teleport short distances. Another could be a physical mutation like growing wings, which might be the result of some ancient bloodline awakening in him through a strange event in the fanfic's plot.