Some fanfic authors like to focus on the emotional aspect of the transformation. They write that Natsu becomes more ferocious and less in control of his emotions, which makes him a more unpredictable and dangerous fighter. This also adds a layer of internal conflict as his friends try to reach the 'human' Natsu within the dragon - transformed state.
One popular interpretation is that Natsu's transformation makes him more in tune with the elements. Since dragons are often associated with powerful elemental magic, in fanfiction, he might be able to control fire in a more refined and intense way. For instance, he could create firestorms that are highly destructive.
In fanfiction, Natsu's dragon transformation often takes on different and exciting aspects. One common element is an enhanced physical strength that far surpasses his normal state. This allows him to take on much stronger opponents with ease. For example, in some fanfictions, he can shatter mountains with a single punch during his transformation.
In some fanfictions where Natsu turns into a dragon, it often gives him extraordinary power. He might have enhanced fire abilities, being able to breathe more intense flames. His physical strength could also increase exponentially, making him an even more formidable force in battles. Maybe he would also gain some dragon - like instincts, which could either help him in combat or cause some internal conflict as he tries to balance his human side with his new dragon self.
Mirajane is a popular choice too. She has a mysterious side to her, and in the fanfictions, she could use her unique abilities to help Natsu or be involved in the events that the Fairy Tail members are watching. Also, Laxus might be included. His powerful magic and complex character can add depth to the fanfiction stories, especially when his relationship with Natsu and the rest of the guild is explored.
Often, Natsu becomes more confident. With the Dragon Force, he realizes his greater potential, which boosts his self - assurance.
One popular trope is the 'fish out of water' scenario. When Natsu and Wendy are sent to a different time, they have to adapt to the new time period's customs and magic usage. For example, in some fanfics, they might find that certain types of magic were more or less powerful in the past. Another trope is the 'changing the future' aspect. They often try to fix something that went wrong in their original timeline, which leads to all kinds of interesting plot twists. And of course, there's the 'reunion with past selves or friends' trope. Meeting younger versions of their friends or themselves can be both heartwarming and full of drama.
Well, in many of these fanfictions, the theme of magical discovery together is quite popular. They both are mages in Fairy Tail, so authors like to write about them finding new spells or magical artifacts while also strengthening their bond. And then there's the theme of protecting each other. Natsu is a very protective character, and in fanfictions with Lisanna, this trait is often emphasized as he defends her from various threats. Lastly, the theme of family acceptance can be seen. Since the Fairy Tail guild is like a family, fanfictions might explore how the other guild members react to their relationship and how Natsu and Lisanna deal with it.
The popularity might be due to the character of Natsu. He is a very dynamic and popular character in the Fairy Tail series. Fans love to explore different scenarios and relationships involving him.
One interesting plotline could be Natsu discovering new dragon powers that are unique to him. This could lead to him having to learn how to control these powers and facing challenges within the Fairy Tail guild as others may be wary or envious of his new abilities.
Another plot twist could be the revelation of a hidden connection between Natsu's dual dragon slayer powers and an ancient prophecy. Maybe it was foretold that a dual dragon slayer would be the key to saving the world from a great evil, but also that this same person could bring about destruction if not guided properly. This would add a lot of moral and ethical dilemmas for Natsu and his friends.
One idea could be that in fanfiction, Natsu's Dragon Form could have unique fire abilities. For example, he might be able to create different shapes of fire, like a dragon made entirely of fire that can attack enemies on its own. Another could be that his Dragon Form has a connection to an ancient magic that gives him the power to heal other dragons or dragon slayers.