The devil could be a new, mysterious character created specifically for the fanfiction. It might be an ancient evil entity that has been lurking in the shadows of the Naruto world for ages.
Perhaps the deal is made by a desperate artist who wants to become the greatest in the world. In return for his soul, the devil gives him the power to create masterpieces that can come to life. But every time he uses this power, a part of his humanity slips away, and he has to struggle with whether the price was worth it.
It could be a new character created specifically for the fanfic. Maybe a powerful and malevolent spirit that has been lurking in the shadows of the Naruto world.
In 'A Deal with the Devil' short story, it often involves a character making a pact with the devil for some desired outcome. Usually, the devil offers something tempting like wealth or power. However, there are always hidden costs and consequences. For example, the character might lose their soul in the end. This type of story is a classic moral tale, warning people about the dangers of greed and making unethical bargains.
The concept of 'deal with the devil' often involves a person making a pact with a devil or some malevolent supernatural being. In many tales, a desperate individual, usually seeking power, wealth, or knowledge, offers their soul in exchange. For example, in the legend of Faust, he made a deal with Mephistopheles. Faust was granted his desires for a time but ultimately faced a tragic end as the devil came to claim his soul. It's a cautionary theme about the high price of getting what you want through unethical means.
Well, Harry Potter himself would be a main character of course. Since it's about him dealing with the devil, he's at the center of the story. Then there would likely be some sort of devil - like figure. It could be a new dark entity created just for this fanfiction or it could be a darker interpretation of an existing character, like Voldemort being given more devilish traits.
Well, perhaps Naruto makes the deal to save his friends. He might trade his future or part of his soul to the devil in this fanfiction. And then he has to struggle with the consequences, like dealing with the devil's constant demands or trying to find a way to break the deal without losing everything.
Another plot twist could be that Naruto discovers that the deal he made with the devil was a setup by an even greater enemy. So, while he thought he was getting power or knowledge from the devil to help his friends and the village, it was all part of a larger scheme to bring chaos. He then has to find a way to break the deal without losing his soul or something equally important.
Add a lot of mystery. Don't reveal all the details of the deal right away. Let the readers wonder what exactly the devil is getting out of it and what the full implications of the deal are for the character. For example, if the deal is about getting revenge on someone, make the revenge seem simple at first but then show how it spirals out of control.
Perhaps in the fanfiction, Harry deals with the devil to gain knowledge about Voldemort's weaknesses. He might be at a desperate point in the fight against the Dark Lord and sees this as his only option. However, the price could be something like losing his connection to his parents' magic. This would lead to a journey of self - discovery as he tries to find new ways to fight without that power.