One possible reason could be that he has had some extremely traumatic experiences with certain ninjas. Maybe he witnessed a powerful ninja going on a rampage and killing innocent people, which left a deep scar in his mind, making him fear ninjas in general.
No. Naruto fanfiction usually involves exciting adventures, battles, and the development of characters. The idea of being afraid of the dark seems a bit out of place. But if someone were to write a fanfic about it, it could be a really creative exploration. For instance, they could write about a young Naruto who discovers a strange jutsu that only works in the dark and he has to overcome his fear to master it. This could be a great way to show his determination and growth as a character.
Yes, there might be. The Naruto fandom is quite large and diverse, so it's likely that there are fanfictions exploring the concept of Naruto being afraid of Kushina. You can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own.
In some fanfictions, Naruto might be afraid of doctors because of past traumas related to medical treatment. Maybe he had a bad experience during a recovery process, like a painful treatment that left a psychological mark.
One reason could be the fear of losing his friends. Naruto has always been very protective of his comrades. In some fanfictions, he might face a situation where he is on the verge of losing them, like a powerful enemy threatening to kill them all. This would make him afraid as his friends are his most precious things.
Well, it could be that Naruto's newfound fear makes him hesitant in battles. He might struggle to use his usual jutsus because he's afraid of the potential consequences. For example, he could be afraid that his Rasengan might cause more destruction than intended and harm innocent people. So, in battles, he'd be constantly second - guessing himself, which would make for an interesting plot as his friends try to figure out what's wrong with him and help him overcome this fear.
One possible plot is that Naruto accidentally awakens a memory or power related to Kushina that is so overwhelming and intense that it makes him afraid. He then has to deal with this new - found fear while also trying to understand his mother better. It could also involve him having to face Kushina in some sort of spiritual or dream - like encounter and being terrified.
Perhaps in the fanfiction, Naruto's fear of the dark is linked to a past traumatic event. For example, he was once trapped in a dark, sealed space during a fight with an enemy. In the story, his friends notice his unease in the dark and they try to help him. Sakura might use her medical ninjutsu to calm his nerves, and Sasuke could use his Sharingan to provide some light. Eventually, Naruto starts to work on facing his fear head - on with their support.
One reason could be a past bad experience. Maybe he had a really painful treatment as a kid that left a deep mark. For example, if he had a serious injury once and the doctor was rough while treating him, it would make him fear doctors.