There could be such a fanfiction. The world of fan - created content is full of surprises. Writers might be inspired to give Naruto the power of Hamon for several reasons. It could be to create a more complex power system in the Naruto world, or perhaps to introduce a new type of threat that only Hamon can counter. Maybe they want to see how Naruto's friends and foes would react to this new ability. So, while I can't say for sure, it's very likely that it exists out there in the sea of fanfiction.
In a 'Naruto has Hamon' fanfiction, Naruto would likely have a new way to interact with his enemies. Hamon, being a life - energy based power, could give Naruto an edge in close - combat situations. He might discover that some of the chakra - based creatures in his world are vulnerable to Hamon. Also, his relationships with characters like Sasuke could be affected as they try to understand and adapt to this new power of his. The story could explore how Naruto uses Hamon to bring about peace in the ninja world in a different way than just with his regular ninja skills.
A group of power - hungry individuals who see Naruto as a threat to their plans of using Hamon to take over the world. They would constantly send assassins and create obstacles for Naruto.
One idea could be Naruto learning Hamon techniques and using them in his battles against powerful foes. For example, he could combine his chakra with Hamon to create unique attacks.
Well, this black and white cartoon bulldog usually shows a friendly and charming look. It might have a short, stocky body and a distinctively stubborn expression. Also, its black and white color combination could add to its unique charm.