Emotionally, Natsu could become more empathetic. If he meets characters in the dark guild who had a difficult past that led them to the dark side, he might start to see things from their perspective. This doesn't mean he would support their actions, but he would understand them better. For example, if there's a character in the dark guild who was orphaned and turned to dark magic for survival, Natsu might feel sympathy for them and try to offer an alternative path rather than just attacking them. This would show a more mature and compassionate side of his character that wasn't as prominent before.
Natsu's character development in this fanfiction might involve him becoming more responsible. With his end form, he has greater power and with that comes the need to use it wisely. He could start to think more about the consequences of his actions. For example, he might not rush into battles as blindly as he used to. Also, his emotional growth could be a part of it. He could become more in tune with his feelings towards his friends, especially Lucy. His loyalty to the guild could also deepen as he realizes his new form can be a great asset to protect Fairy Tail.
Often, Natsu becomes more confident. With the Dragon Force, he realizes his greater potential, which boosts his self - assurance.
At first, they might be in disbelief. The members of Fairy Tail see Natsu as a core part of the guild, so it would be hard for them to accept that he has betrayed them. They would probably try to talk to him and find out what's going on. Some members might be angry immediately, thinking that he has turned his back on their family. But others, like Lucy, might be more hesitant to believe it and would look for a way to resolve the situation without conflict.
The guild would likely be shocked at first. They consider Natsu as one of their own, so his attack would be completely unexpected. Some members might try to talk him down, like Lucy. She has a close bond with Natsu and would probably try to reason with him.
If Natsu is a girl in this fanfiction, her character might change in terms of her relationships. For instance, she may be more self - conscious about her appearance compared to when she was male. Also, her interactions with male characters like Gray could shift. Instead of their typical rival - like banter, there could be a more complex emotional undertone, like a friendly - rivalry with a hint of romantic tension perhaps.
In some fanfictions, Natsu could be framed by a dark guild as a traitor to Fairy Tail. The dark guild spreads false rumors and evidence, causing Fairy Tail to turn against him. Natsu then has to prove his innocence while also taking on the dark guild that started it all. This would lead to a lot of internal conflict within Fairy Tail and also intense battles between Natsu and the dark guild members.
She would fit in very well. The Fairy Tail guild is all about family and acceptance. Given her parents are Lucy and Natsu, she'd be welcomed with open arms. She could learn from the older members like Makarov and Mirajane, and bond with the younger ones like Romeo. Her magic skills would also contribute to the guild's strength during battles or when helping the town.
In fanfiction, if Natsu turns into a dragon, his character development would be a journey. He would have to face his own self - doubts. As a dragon, he has more power, but with that comes responsibility. He would need to learn how to control his dragon instincts, like aggression and territoriality. This process would shape him into a more mature character. His relationships would also change. Some characters might look up to him more, while others might question his humanity. Through all these experiences, Natsu would grow and become a different kind of hero in the Fairy Tail world.
In this fanfiction, the story might take a darker turn. Natsu is like the heart and soul of Fairy Tail in many ways. Without him, there could be a sense of gloom in the guild. However, this could also be a catalyst for change. Characters like Wendy could step up more. She might start to explore and master her dragon slayer magic in ways she hadn't before. And the relationships between the characters would shift, perhaps becoming more complex as they deal with the absence of Natsu.
Natsu would likely become more responsible. Taking care of a baby is no easy feat, and he'd have to learn things like being gentle and patient, which are not his usual strong suits. This would be a big step in his character growth.