Obviously, Natsu is one of the main characters. He is the strongest dragon slayer in this fanfiction. His friends from Fairy Tail like Lucy, Gray, and Erza are also likely to be main characters. They often support Natsu in his battles and adventures.
Another plot might involve Natsu losing his dragon slaying powers temporarily. He then has to rely on his wits and the help of his friends in Fairy Tail. This could lead to some really heartwarming moments as his friends support him, and also some tense battles where they all have to fight together without Natsu's usual brute strength.
One popular 'natsu strongest dragon slayer fanfiction' is 'The Ascent of Natsu'. It shows Natsu achieving new levels of power and facing challenges that really highlight his status as a strong dragon slayer.
The main appeal is seeing Natsu's character at his most powerful. Fans love to see their favorite character in a position of extreme strength and dominance.
It could be a powerful dark wizard who sees Natsu as a threat because of his alpha status among dragon slayers. This wizard might want to eliminate Natsu to gain control over the dragon slayers or to carry out some evil plan without interference.
There might also be some dark magic - using villains who want to use Natsu's alpha dragon slayer powers for their own evil purposes. They could try to capture him or manipulate him in some way. Maybe they plan to extract his power to create a powerful weapon or something.
Obviously, Natsu is a main character. He is the central figure in most dragon slayer fanfictions. Also, his friends like Lucy, Gray, and Erza often play important roles. They support Natsu in his battles and adventures, and their unique abilities and personalities add depth to the story.
Lucy would be a great character to include. She could help Natsu research about water dragon slayer magic. Gray could also be there, and they could have some friendly rivalries regarding the different elements. Happy would be essential as Natsu's sidekick, providing comedic relief and also helping in some tricky situations.
There could be a young mage who idolizes Natsu and joins him on his adventures. This character could be inexperienced but full of enthusiasm, providing some comical moments as well as opportunities for Natsu to be a mentor.
A powerful dark dragon slayer who has mastered both shadow and ice magic could be a great antagonist. He could be jealous of Natsu's natural ability with fire and his popularity among the guild, and thus wants to prove his superiority.
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.