A young dragon slayer - in - training who idolizes Natsu. This character could be from a far - off land and has heard tales of Natsu's dual powers. They could have their own unique magic related to a different element that complements Natsu's powers.
A mysterious mage who is researching the dual dragon slayer phenomenon. They are neither good nor bad at first, but as the story progresses, they become an ally or a foe depending on their motives. This mage could have the ability to manipulate time or space, which adds an interesting dynamic when interacting with Natsu and his powers.
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.
The Magic Council could be potential enemies. Since Natsu is an outlaw, they would be the ones to try and capture him. Also, dark guilds might see him as a threat or a valuable asset to capture. They could send their strongest members after him.
There could be new human characters as well. Maybe some mages from other guilds who are curious about Natsu's new status. They could either be allies or potential threats. And don't forget about the celestial spirits. Since Lucy is Natsu's friend, the celestial spirits might get involved in some way. They could offer their unique powers or knowledge to help Natsu in his new role as the dragon king.
One idea could be Natsu exploring a new magic ability related to his dual dragon slayer powers. For example, he discovers a way to combine the fire of his Igneel - taught magic with the other dragon's element in a more powerful and unique way.
There could be a wise old mentor who was also a poison dragon slayer in the past. He can guide the main slayer with his years of experience and knowledge about different poisons and dragons.
Potentially, we could see some celestial dragon characters. They might be ancient and powerful beings. Some could be friendly towards Natsu, seeing him as a new hope for their kind. Others might be more hostile, seeing him as an intruder or a threat to their traditional ways. There could also be other mages from different guilds who are either curious or envious of Natsu's situation with the celestial dragons.
Another potential character could be a dragon oracle. This oracle could have the ability to see Natsu's true nature and destiny. They could either help Natsu understand his powers and purpose or be a bit of a trickster, making Natsu's journey to discover himself even more difficult. And of course, the other members of Fairy Tail would be there to support or sometimes misunderstand Natsu as he deals with his dragon - born identity.
In some fanfictions, there might be original characters created by the author. For instance, a mysterious figure who has some connection to Natsu's multi - dragon slayer abilities. This character could be an antagonist, testing Natsu's skills, or a mentor, guiding him to master his powers better.
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.
They can also create characters who are connected to Natsu's past regarding his dual dragon slayer powers. Maybe an old friend or a long - lost relative who knew the secrets behind how he got these powers. These characters can bring out different sides of Natsu, like his more vulnerable or determined side.