Perhaps the fanfic focuses on the origin of Natsu's dragon - like roar. It could explore some hidden power within him that he didn't know about before. The story might involve him trying to control this new - found aspect of his power. And it could also have some sub - plots about his relationships with other characters who are either in awe or a bit scared of his roar.
Obviously, Natsu would be the main character. There could also be his friends like Lucy, Gray, and Erza. They might be either supporting him during his moments when he roars like a dragon or they could be in the vicinity when it happens and react to it in different ways.
Well, perhaps the story could start with Natsu having a strange encounter that begins his transformation into a dragon. Maybe he discovers some ancient magic or a hidden power within himself that is related to dragons.
Well, perhaps the plot could involve Natsu hiding his dragon identity from his friends in the guild. He might be worried about how they'll react if they find out. Maybe there are certain powers that come with being a dragon secretly that he has to learn to control without anyone noticing.
Perhaps the story focuses on the bond between Natsu and the small dragon. The small dragon might have special powers that help Natsu in battles against villains in their magical world. It could also be about how Natsu takes care of the small dragon, teaching it things and growing together in their friendship.
Maybe it could involve Natsu having to go through some really tough trials to prove himself worthy of becoming the Fire Dragon King. For example, he might have to battle powerful enemies that are related to the dragon world's ancient secrets.
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.
Maybe Natsu discovers a new magic spell that accidentally turns him into a dragon. He then has to figure out how to reverse it while dealing with the new powers and instincts.
Well, it could be about Natsu having some sort of special connection to the celestial dragons. Maybe he discovers he has celestial dragon blood in him and has to deal with the powers and responsibilities that come with it. He might also encounter other characters who either fear or revere him because of this newfound aspect of his identity.
One possible plot twist could be that Natsu discovers he has to sacrifice his human memories to fully become the Dragon King. This would create an internal struggle as he values his relationships with his friends in the guild. Another twist might be that there are other hidden dragon powers within him that are awakened only when he starts the transformation process, powers that no one expected.
One possible plot could be that Natsu, while being raised by the female dragon, learns unique dragon magic that is different from what he would have learned otherwise. He might develop a special bond with the dragon, like a mother - son relationship, and the story could follow his adventures as he uses the skills taught by the dragon to protect the dragon's lair or the surrounding area from threats.