One possible reason could be a powerful enemy's fire - based jutsu. For example, if Naruto is facing a skilled fire - style user like Sasuke during a battle gone wrong, Sasuke's powerful fire techniques might accidentally burn Naruto.
A rogue ninja from a rival village could be responsible. They might see Naruto as a threat and use their fire - based attacks to harm him. For instance, a ninja from the Hidden Mist Village who has a grudge against Konoha and targets Naruto specifically.
Well, 'naruto burned fanfiction' might be a fanfic that focuses on a particular event in Naruto where there's destruction by fire. Maybe it's about a village getting burned down and how the Naruto characters deal with it. It could explore themes of loss, survival, and rebuilding in the context of the Naruto world.
You can try looking on popular fanfiction websites such as Fanfiction.net or Archive of Our Own (AO3). Just use their search functions and type in 'naruto burned' to see if any relevant stories pop up.
He might become more withdrawn. The burned face could make him self - conscious, so he doesn't interact as freely as before. For example, he might avoid public gatherings or eye contact with people.
One possible plotline could be that Naruto is caught in a powerful enemy's fire - based jutsu during a battle. Maybe the enemy has some vendetta against him and wants to see him suffer. Another could be that Naruto sacrifices himself by jumping into a burning building to save civilians. He might then struggle to survive the intense heat and his injuries.
One idea could be that Naruto gets his face burned during a battle against a new and powerful enemy. He then has to deal with the physical pain as well as the psychological impact. People in the village might react differently to his changed appearance, some with pity and some with fear.
Show the reactions of his friends. If Naruto is burning alive, how do Sasuke, Sakura, and the others respond? Their desperation, their anger at not being able to save him easily can really tug at the heartstrings. You could also include flashbacks of their times together, making the loss seem more real and tragic.
It could mean that in the Naruto universe or among Naruto fans, someone named Naruto (or a character representing Naruto) destroyed a fan - created fictional work that was still ongoing or 'live'. Maybe it was a fanfic that violated some unspoken rules or ethics within the fan community.
It could mean that there is some fanfiction related to Harry Potter that has been destroyed, perhaps literally burned. Maybe it's part of a story where someone is getting rid of unwanted or dangerous fanfiction in a very extreme way.