In many of these fanfictions, the way Natsu's dragon form affects his relationships is a big plot point. For example, his enemies might be more afraid of him, or his friends might see him in a new light. Also, the use of his dragon form in battles against powerful villains can be really engaging. His new abilities could give him an edge in combat that he didn't have before, like breathing fire in a more powerful way or having enhanced strength and speed.
A great fanfiction to check out is 'When Natsu Became a Dragon'. This one focuses a lot on the emotional aspect of Natsu turning into a dragon. It shows his inner turmoil and how his friends react to this new side of him. There are some heart - warming moments as they all try to understand and support Natsu through this transformation.
It could be a water - based dragon. In that case, Natsu might have some water - related magic in addition to his fire magic. This would make him a very unique character as he would be able to combine two opposing elements in a way that no one else in the Fairy Tail guild could.
There probably is. Fanfiction allows for all sorts of wild and creative ideas. Given Naruto's own abilities to transform, like his Nine - Tails form, it's not too far - fetched for a fan to write a story where he can turn into a dragon. You could try searching on popular fanfiction websites using relevant keywords to find such a story.
Gray might show up too. He could start as a bit of a rival, not believing that Natsu can really achieve great things with this Dragon God training. But as the story progresses, he could become more of a supporter. And then there's Lucy. She might be worried about Natsu during the training, and also use her celestial spirit magic to help Natsu in some unexpected ways during his training, like summoning spirits that can provide unique challenges for Natsu to overcome.
Potentially, we could see some celestial dragon characters. They might be ancient and powerful beings. Some could be friendly towards Natsu, seeing him as a new hope for their kind. Others might be more hostile, seeing him as an intruder or a threat to their traditional ways. There could also be other mages from different guilds who are either curious or envious of Natsu's situation with the celestial dragons.
Happy, Natsu's flying cat companion, would definitely be a main character. He would be there to provide comic relief as always, but also be a source of emotional support for Natsu during his transformation into a dragon god. Erza might also be a prominent character. With her strong leadership skills and powerful magic, she could be guiding the guild during the times when Natsu is still coming to terms with his powers and the changes it brings to the guild.
One common reason could be a curse. Maybe they unknowingly violated some ancient rule or pact while slaying dragons, and as a result, a curse is placed upon them that gradually transforms them into the very creatures they hunt. For example, they might have desecrated a dragon's lair that was protected by a powerful magic.
In the 'king of dragon slayer fanfiction', Natsu is likely a central figure. He might have special powers related to slaying dragons, like breathing fire or having enhanced strength. His character could be developed in ways that are different from the original series, perhaps with new relationships and challenges within the fanfiction world.
A popular one is 'Dragon's Love for the Celestial Mage'. This fanfiction takes their relationship to a new level. It starts with a simple adventure but soon unfolds into a story of deep love and loyalty. The author does a great job of portraying Natsu's dragon - like instincts when it comes to protecting Lucy, and Lucy's growing feelings for Natsu are also well - written.