Even a misdirected ally could be the cause. If during a chaotic battle, a fellow Konoha ninja's fire - based jutsu goes astray, it might end up hitting Naruto and burning him.
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.
It could be a character who has been corrupted by dark powers. This character, once a friend or acquaintance, might turn on Naruto and use fire to attack him. Perhaps someone who has fallen under the influence of Orochimaru's dark experiments.
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 new and powerful rogue ninja could be responsible. This ninja might have a vendetta against Konoha and see Naruto as a symbol of the village, so they target him and use their strong and devious techniques to injure him badly.
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.
Obviously, Lucy is one of the main characters since the fanfiction is centered around her getting burned. There might also be characters like her family members, such as her parents or siblings, who could play important roles in her recovery process.
Sasuke could be a possible cause. If Sasuke were to go back on his word about protecting the village or if he were to harm their friends again, Naruto would be pissed. Their relationship is complex, and Sasuke's actions often have a strong impact on Naruto.
It could be Orochimaru. He's always been interested in power and experimenting. Maybe he sees Naruto as a perfect guinea pig to test some new jutsu that goes horribly wrong and causes Naruto to explode.
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.
Well, it could be a new inmate who sees Michael as a threat and decides to undermine him. This inmate might spread rumors or false information to get Michael in trouble.
It could be a rival from another house. For example, a jealous Slytherin who wants to take Ginny out of the Quidditch game. They might use some underhanded tactics to make her broom malfunction and cause her to get hurt.
Maybe it's a human who has somehow discovered the world of demigods and is afraid of their existence. They shoot Annabeth out of fear and misunderstanding. Another option is that it's a rogue demigod who has gone bad and is working against their own kind. This character could have a personal grudge against Annabeth specifically, perhaps because of her intelligence and leadership skills which they envy.