One idea could be Natsu discovering new and more powerful fire-based spells as a Fire God Slayer. Maybe he has to face a powerful ice - based enemy that forces him to tap into deeper levels of his god - slayer magic. This would make for an exciting action - filled fanfiction.
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.
One possible plot could be that Natsu discovers his new power as a war god slayer magic user. He then has to face a series of powerful enemies who are threatening the world. Along the way, he might meet new allies who also have unique magic abilities. As he battles these foes, he gradually masters his war god slayer magic and becomes a more powerful wizard.
It could be another powerful mage who is jealous of Natsu's new war god slayer magic and wants to steal it for himself. This mage might have been researching ways to gain such powerful magic for a long time and sees Natsu as an obstacle to his own plans.
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.
A good plot twist could be that Natsu's Fire God Slayer magic is actually a curse in disguise. It was given to him by an evil entity that wants to use him for its own purposes. This would completely change the direction of the story and add a lot of mystery.
One great fanfiction could be 'Natsu's Ascent'. In this, Natsu discovers new powers as a third - generation dragon slayer and goes on a journey to find a hidden dragon lair. It has a lot of action and great character development.
Well, in fanfiction, Natsu as an alpha dragon slayer can have a different relationship with his dragon side. He may have more control over it or be able to access more of its power. His personality might also become more assertive. He doesn't shy away from taking charge, whether it's in a fight or in coming up with plans to solve problems. He may also have some new abilities that are unique to his alpha status, like being able to sense danger from farther away or having a special connection with other alpha - like beings in the magical realm.
Natsu might be considered the alpha in dragon slayer fanfiction because of his strong leadership skills. He often takes charge in difficult situations and his comrades look up to him. His determination and unwavering will to fight also contribute to this perception.
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.