Another potential character could be a dragon oracle. This oracle could have the ability to see Natsu's true nature and destiny. They could either help Natsu understand his powers and purpose or be a bit of a trickster, making Natsu's journey to discover himself even more difficult. And of course, the other members of Fairy Tail would be there to support or sometimes misunderstand Natsu as he deals with his dragon - born identity.
Well, perhaps it could be about Natsu having some special powers right from birth that are related to dragons. Maybe he can communicate with dragons in a unique way that no one else can since he was born with this dragon - like essence.
Obviously, Natsu would be the main character since it's about him being born a dragon. His friends from Fairy Tail like Lucy, Gray, and Erza are likely to be important characters as well. They would probably play a role in how Natsu adapts to his new form.
A possible plotline is that Natsu's dragon form attracts the attention of dark wizards who want to use his power for evil. So he has to fight against them while also coming to terms with what it means to be a dragon. He may also have to deal with the physical and mental changes that come with this transformation, like different instincts and a new way of seeing the world.
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.
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.
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.