It could be that there was some sort of magic involved. Maybe an enemy of Thranduil cast a spell that made the dragon more aggressive towards him. The dragon fire might have some special properties due to this magic, and Thranduil's burns could be not just physical but also have some sort of curse or negative effect on his being. He then has to find a way to break the curse while dealing with his injuries.
He might become more cautious. After experiencing the pain of the dragon fire, he could be more hesitant in engaging in battles, especially those involving dragons. This could change his military strategies.
One interesting fanfiction could be where Thranduil uses his elven magic to counter dragon fire. Maybe he creates a shield of ancient elven power that not only withstands the intense heat but also reflects the fire back at the dragon. This would show his great power and wisdom as an elven king.
Another place to look is Archive of Our Own (AO3). There are a lot of talented writers in the Tolkien fandom there. A good fanfiction might involve Thranduil having to protect his people from a dragon's fire. Maybe the dragon has been awakened by some dark magic and Thranduil is the only one who can stop it. The fanfiction could explore his character development as he overcomes this great threat.
One possible scenario could be that Harry is tricked by a dark wizard into believing that his friends are in danger if he doesn't betray the rules of the Goblet of Fire. Maybe he's shown false visions of Ron and Hermione being tortured, and in his panic to save them, he does something that goes against the fair play of the tournament, like getting inside information about the tasks through improper means. Another could be that he's under the influence of a powerful potion or spell that makes him act against his normal values and betray the trust placed in him regarding the tournament.
One common theme is power dynamics. Since Thranduil is a powerful elf king and dragons are also very powerful creatures, their interactions often involve a struggle for power or respect. Another theme is mystery. Dragons are often mysterious in these stories, and Thranduil tries to figure them out.
A story about a fire could have a person reflecting on their life while fighting the flames. It could also show the heroic efforts of multiple fire departments collaborating to put out the blaze. Or perhaps there's a love story that blossoms amidst the chaos of the fire.
In this 'Chicago Fire' fanfiction where Gabby gets hurt, it could start with her being overconfident in a dangerous situation. For example, she might enter a burning building without proper backup. As she progresses deeper into the building, the fire intensifies rapidly. She could trip over some rubble in the smoky environment and sprain her ankle. Then, as she tries to get up, a part of the ceiling might come crashing down on her. This would leave her seriously injured and in need of immediate rescue. Her fellow firefighters would then have to race against time to find her and get her out of the building safely.
One possible scenario could be that during a rescue operation, there's a sudden collapse of a building. Brett might be in the wrong place at the wrong time and get hit by falling debris, injuring her leg or back severely. This would not only put her in physical pain but also cause emotional distress among her colleagues who care about her.
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.
One possible scenario is that Naruto is in a fight against a very strong enemy. He realizes that his normal attacks are not effective, so he taps into the black fire power. He then uses it to overpower his foe with its intense heat and destructive force.