Well, in 'natsu is a dragon god slayer fanfic', themes like growth and evolution are very common. Natsu's character is growing not just in terms of power but also in his understanding of the world around him. Family is also a theme that pops up. Since dragons are like family to him in a way, his connection to them and how it affects his actions is explored. And of course, the theme of heroism. Natsu is seen as a hero, especially with his new powers as a dragon god slayer, and how he lives up to that role, facing challenges and saving the day, is a big part of these fanfics.
Power and responsibility is a common theme. As Natsu becomes a dragon god slayer, he has more power, but also more duties. Another theme is friendship. His friends in Fairy Tail still support him even as he changes. And there's often the theme of self - improvement, as Natsu has to master his new abilities.
One popular 'natsu is a dragon god slayer fanfic' might be 'Natsu's Ascent'. In this fic, Natsu's journey as a dragon god slayer is filled with intense battles and character growth. Another could be 'The Dragon God Slayer's Legacy' which delves into how Natsu's new powers affect his relationships with his guildmates. There's also 'Natsu: Dragon God Slayer Reborn' that takes a different turn on his origin story as a dragon god slayer.
One great 'Fairy Tail Natsu Dragon God Slayer' fanfiction is 'The Dragon's Ascent'. It really delves into Natsu's growth as a Dragon God Slayer in a unique way. The author creates new challenges for Natsu that are both exciting and in - line with the Fairy Tail universe.
Another aspect is the world - building. Since it's set in the Fairy Tail universe, the fanfiction should expand on the existing lore. Maybe introduce new dragons or aspects of the Dragon God Slayer magic that we haven't seen in the original series. This makes the fanfiction feel like a natural extension of the Fairy Tail world.
I've also heard of a fanfiction titled 'The New Era of Natsu, the Dragon God Slayer'. This fanfic focuses on Natsu's journey after becoming a dragon god slayer. It has a lot of elements of self - discovery. Natsu has to learn how to control his new powers and face enemies that are far more dangerous than before. The author does a great job of creating a vivid world around Natsu's new identity.
In addition to Natsu, Wendy could be a main character in the 'natsu is a dragon god fanfic'. Since she also has dragon - related powers, she could have a special connection with Natsu in this new situation. Maybe she helps him understand more about his dragon god powers. And Makarov, as the guild master of Fairy Tail, would also be a significant character. He would be concerned about how Natsu's new status affects the guild and the magical world as a whole.
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.
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.
An ancient dragon that has turned evil due to some dark magic could be the main antagonist. This dragon might see Natsu as a threat because of his unique combination of powers and wants to eliminate him. Natsu would then have to use all his skills and the help of his friends to fight this dragon. The dragon could also have minions that are constantly causing trouble for Natsu and his guild.