Well, if Naruto finds a gun in a fanfiction, it would be really out of place in the ninja world he's from. But he might be confused at first. He'd probably try to figure out what this strange object is, since it's so different from his shurikens and kunai. He might even accidentally set it off, causing chaos in the village.
Well, it depends on the context of the fanfiction. If it's set in a more modern - ish Naruto world, perhaps Naruto would see the machine gun as a new and powerful tool. He might take it to his friends at Konoha to study it together. Sakura, being the intelligent one, could try to analyze it while Naruto is eager to test its power against some powerful foes. However, this would also bring up questions about the balance of power in the Naruto universe.
In a 'Naruto finds a gun' fanfic, one possibility is that Naruto, being curious, might initially mistake it for some strange new weapon from another land. He could try to figure out how it works in his own Naruto - like way, perhaps by trying to infuse chakra into it, which might lead to unexpected and comical results, like the gun shooting out chakra - blasts instead of bullets.
In the 'naruto finds a gun' fanfic, Naruto may initially be excited by the novelty of the gun. But as he discovers its power, he could become more serious. His usual carefree and impulsive nature might be tempered. He would have to think twice before using it, as it has the potential to cause great harm. This could lead to a transformation in his character, making him more responsible and less reckless in combat situations.
One possible fanfiction could be about Kushina finding Naruto in a situation where he's lost in a forest. Maybe she uses her unique chakra sensing abilities to track him down. It could be a heartwarming story of a mother reuniting with her son.
One possible scenario in this fanfiction could be that Naruto discovers an ancient and mysterious shrine in the forest. The shrine might hold some sort of power or secret. Maybe it has a connection to the Sage of Six Paths. Naruto, being his curious self, would likely start to explore it. He might find strange markings or artifacts inside that he has never seen before.
One common plot is Kushina finding Naruto in a different time or dimension. For example, she might end up in the future where Naruto has grown up and she gets to see the kind of person he has become. It's an emotional and interesting concept as she gets to witness all his achievements and the challenges he has overcome.
One idea could be that the baby is from a hidden clan. Naruto decides to protect the baby from those who would use its special abilities. He takes the baby under his wing and trains it as it grows up, passing on his ninja values.
Yes, there are likely fanfictions out there with this concept. Fanfiction writers often like to cross over different popular franchises. Naruto and Pokegirl are from two very different universes, so it makes for an interesting and unique combination in fanfiction. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own to find such stories.
One idea could be that Naruto mistakes the spaceship for a really strange summon. He tries to communicate with it using his ninja skills, like sending chakra signals, thinking it's some sort of new, unknown creature. This could lead to all sorts of comical misunderstandings as the spaceship's technology reacts in unexpected ways to his attempts.