Yes, there might be. There are numerous fanfiction platforms out there where such a concept could exist. However, you may need to search through popular fanfiction sites like Fanfiction.net or Archive of Our Own to find it specifically.
A really cool Naruto Hellhound fanfiction idea could be that the Hellhound is actually a cursed form of a powerful ninja. Naruto has to find a way to break the curse. This could involve a journey where Naruto discovers ancient secrets about the Hellhound's origin and uses his own ninja skills and strong will to free the being trapped inside the Hellhound form.
First, think about the Hellhound's characteristics. Maybe it has fire - breathing abilities or can teleport. Then, find a unique way to integrate it into the Naruto world. For example, it could be related to a new type of chakra. Also, create a strong plot. It could be a mystery where the Hellhound is the key to solving something big in the Naruto universe.
In a 'Naruto is a Hellhound' fanfiction, you might see Naruto's personality being influenced by the Hellhound aspect. He could be more aggressive or have a stronger sense of loyalty, which are often associated with Hellhounds. The story could also introduce new characters or enemies related to the Hellhound lore. There might be a whole new world or dimension that Naruto has to navigate as a Hellhound, which could bring in different kinds of challenges and adventures compared to the original Naruto storyline.
Well, in some fanfictions, the hellhound summoning contract could lead to a whole new set of adventures. The hellhounds might have their own society or hierarchy, and the main character has to navigate through that while also dealing with the normal Naruto - type challenges like fighting other ninja clans or protecting their village.
It could be a side character from the original Naruto series who wasn't given much spotlight before. They find the hellhound summoning contract and it changes their role in the story completely. For example, a previously weak or overlooked ninja suddenly becomes a force to be reckoned with thanks to the hellhounds.
In a fanfiction, the hellhound could be a protector of Percy instead of an enemy. It could be that the hellhound was once a pet of a powerful god who turned evil, and Percy helps it break free from the evil influence. So the hellhound then becomes loyal to Percy and helps him in his quests, like warning him of approaching monsters or even fighting alongside him against stronger foes.
One possible scenario in a Harry Potter pet hellhound fanfiction could be that a student secretly adopts a hellhound puppy. They manage to keep it hidden in the Room of Requirement. The hellhound grows up with a special bond to the student, and it eventually helps them during a dangerous encounter in the Forbidden Forest, using its fierce loyalty and powerful abilities.
There's also a fanfic where a hellhound becomes a protector of Percy's sister. In this 'Percy Jackson Hellhound Fanfiction', the hellhound's loyalty and the way it interacts with the characters in the Percy Jackson universe are really interesting. It shows a different side of these usually menacing beasts.
Fanfiction.net is a great place to start. There are tons of 'Percy Jackson Hellhound Fanfiction' there. You can search by tags like 'hellhound' and 'Percy Jackson' to narrow down the results.