It could be a rogue wizard who has also acquired Muggle weapons and is using them to cause chaos. This wizard might be jealous of Harry's fame and wants to use the gun to prove that he's more powerful.
In this fanfiction, Harry might have the gun as a gift from a mysterious figure. The gun could have special powers like it can only be fired by him and the bullets can penetrate any protective spell. This would lead to a whole new set of adventures as he tries to figure out the origin and purpose of this unique weapon.
A wizard who has dabbled in the Muggle world might give Harry a gun. This wizard could have seen the potential use of a Muggle weapon in the wizarding world's dangerous situations.
It's possible that there's a hidden stash of Muggle items in Hogwarts, and Harry stumbles upon it. He discovers the gun there, realizes it could be a powerful weapon against Voldemort, and decides to use it.
Some might be shocked. Hermione, for example, would probably be very concerned about the use of a Muggle weapon in the wizarding world and its implications. She might worry about how it could change the balance between the Muggle and wizarding communities.
Well, it would be a very strange and interesting scenario. He might use the gun in a way that combines magic and Muggle weaponry. For example, he could use magic to enhance the gun's power or accuracy. Or perhaps he would be in a situation where his usual magic is restricted and the gun becomes a new way to defend himself and his friends. It could also lead to some very different interactions with the villains in the story, as they might not expect a wizard to be armed with a Muggle weapon.
The idea of Harry Potter with a gun is quite interesting. One possibility is that he gets the gun from the muggle world accidentally. He might initially be confused about how to use it but then realizes its potential. This could lead to new alliances in the wizarding world. Some wizards might be intrigued by this new weapon and want to learn more about muggle technology, while others might be afraid and try to confiscate the gun from Harry.
In the 'harry gets a gun fanfiction', it could be that Harry is given the gun by a mysterious figure. This figure might have an ulterior motive, like using Harry as a pawn in a bigger game. Harry then has to decide whether to trust this person and what the implications of having the gun are for his own safety and the safety of those around him.
He could have been influenced by the Muggle world. Having grown up with Muggles, he might have seen the power of guns and thought it could be a more straightforward solution compared to complex magic spells. Also, he might have wanted to prove that Muggle technology could be just as effective in the wizarding world's battles.
In a 'Naruto has a gun' fanfiction, the plot could involve Naruto getting the gun during a mission in a foreign land. The gun could be a symbol of power there. Naruto then has to face the moral dilemma of using such a weapon. He might face enemies who are also after the gun because of its power. His ninja skills would be combined with the new threat and advantage of the gun, leading to some intense battles and strategic decisions.