There could also be some new characters introduced specifically for this fanfiction. For instance, an ancient dragon who knows all about Natsu's true nature and acts as a mentor to him. This dragon could have a complex backstory and motives, and its interactions with Natsu and the other Fairy Tail members would be a major part of the story.
Gray would also be important. There could be a rivalry - turned - friendship aspect where Gray, who has his own ice - making powers, and Natsu, as a dragon, have to learn to work together. Maybe they compete in a friendly way to see whose powers are more useful in different situations.
Lucy could be part of the story too. She might befriend the small dragon and use her celestial spirit magic to help Natsu and the small dragon in their adventures. There could also be some evil characters like Zeref who might try to use the small dragon for his dark plans.
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.
Erza is also a main character. She is a strong and independent warrior, often leading the group and providing a sense of discipline among the dragon slayers.
There could be other Fairy Tail members as main characters too. They might play important roles in Natsu's new adventures. For instance, Lucy could be there to support Natsu with her celestial spirit magic. Gray might also be involved, adding his ice - make magic to the mix and having some interesting interactions with Natsu's new dragon - related situations.
Natsu would definitely be one of the main characters since the title implies he is the alpha dragon. There might also be his friends from the original series, like Lucy, Gray, and Erza. They could play important roles in how they interact with Natsu in his new form.
Obviously, Natsu would be the main character since it's about him being born a dragon. His friends from Fairy Tail like Lucy, Gray, and Erza are likely to be important characters as well. They would probably play a role in how Natsu adapts to his new form.
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.
Lucy could be a main character. She was always close to Natsu in the original Fairy Tail. So when Natsu returns as an 'ex' and meets the guild again, she would likely play a big role in how he is received and in the development of the story.
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.