Yes, there might be. Fanfiction is a vast world with all kinds of creative and unique ideas. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in 'Naruto allergic to copper kunai' in their search bars and see what comes up.
Well, perhaps the plot could start with Naruto noticing strange symptoms whenever he's near copper kunai. As the story progresses, it's revealed that this allergy is not natural but was somehow inflicted on him by an enemy. This enemy uses this knowledge to their advantage in battles. Naruto, along with his friends, has to search for a way to reverse the allergy. They might journey to find a rare herb or consult an old sage who knows about such curses. Along the way, Naruto has to develop new fighting techniques that don't rely on kunai at all.
In some fanfictions, Minato saves Naruto physically. For example, he might use his teleportation jutsu to appear right in the middle of a fight and whisk Naruto away from danger. In others, he could save Naruto spiritually. He might enter Naruto's mind, like in the fanfic 'Minato's Mind - Saving Mission', and give him the strength and confidence to overcome his inner demons. Sometimes, Minato saves Naruto from a political situation. For instance, in 'Minato and the Hidden Leaf's Politics', he uses his influence and wisdom to protect Naruto from being used as a political pawn.
Well, it depends on the specific fanfic. Some fanfics might really emphasize Naruto's growth to be on par with Minato in terms of smarts. They could show Naruto learning from Minato's memories or having some sort of spiritual connection that transfers knowledge. However, other fanfics might focus more on other aspects of Naruto's character and not necessarily make him as smart as Minato.
The relationship can be developed by having Minato appear in Naruto's memories more vividly. For example, Naruto could start having flashbacks of Minato's training sessions or family moments that he didn't know about before. This would make Naruto feel closer to his father.
Minato might show his protectiveness by always being near Naruto in spirit. For example, he could leave behind some kind of jutsu or power that activates when Naruto is in great danger, like a hidden seal that releases a powerful defense.
Minato could be possessive of Naruto in fanfiction due to his guilt. He feels guilty for leaving Naruto alone in the world without his parents. This guilt might manifest as possessiveness, as he wants to protect Naruto from any harm and be the father he never got to be before. He wants to be the only one to guide and care for Naruto, thus showing possessive behavior.
Yes, there might be. The Naruto fandom is quite large and diverse, so there could be fanfictions exploring such dark and alternate scenarios. However, these often deviate from the original positive relationship portrayed in the official series.
In fanfiction, Naruto and female Minato could have a really interesting dynamic. For instance, Minato's femininity might bring out a different side of Naruto's character. He could be more protective of her, or she could inspire him in new ways. Maybe she has a special way of seeing the world that Naruto starts to adopt, leading to his growth as a ninja.
One possible aspect of a Naruto and female Minato fanfiction could be exploring an alternate timeline. Maybe in this story, Minato was born as a female and still became the Fourth Hokage. Her relationship with Naruto would be very different, perhaps more maternally strong. She could teach Naruto unique jutsu that she developed as a female ninja, which might have different elements compared to the male Minato's techniques in the original story.