Another way would be for Natsu to go through a great deal of self - discovery and remorse. He could then strive to rebuild the guild in the image of what it once was, and through his efforts, the remaining guild members could come to forgive him. This would be a long and difficult journey for Natsu, but it could potentially redeem the story and bring it back to the themes of friendship and hope that are so important in Fairy Tail.
One way could be through some kind of time - travel or alternate reality plot. For example, Natsu could find a way to go back in time and prevent his actions. This would allow the story to get back to the more positive and friendly tone of the original Fairy Tail.
One possibility could be that Natsu is under some sort of dark magic influence. Maybe a powerful enemy has managed to control his mind, making him turn against the guild master. Another reason could be a misunderstanding. If some false information is fed to Natsu about the guild master being a threat to the guild or his friends, his hot - headed nature might lead him to take drastic action without fully understanding the situation.
The guild would be in chaos. The members would be shocked and divided. Some might side with Natsu if they believe there was a just cause, while others would see him as a traitor. There would be a power vacuum, and different members might vie for the position of guild master. This could lead to internal strife and potential break - up of the guild.
Well, in fanfiction where Natsu leaves the guild, he could become a sort of lone wolf. He might travel to far - off lands to discover more about his dragon - slayer powers or his past. This could lead to him meeting new and powerful allies or enemies. Without the support of the guild, he would have to rely solely on his own strength and wits. It could also make him a more serious and hardened character, as he no longer has the safety net of his Fairy Tail family.
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.
One possible antagonist could be a dark wizard from a rival guild who is jealous of Natsu's status as an alpha in Fairy Tail. This wizard might try to undermine Natsu's leadership and the guild's reputation.
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.
It could be a rogue wizard who has a vendetta against Natsu and somehow manages to manipulate the Fairy Tail guild. This wizard might have lost to Natsu in the past and is now seeking revenge in a devious way by turning his own guild against him.
One possible reason could be a misunderstanding. Maybe Natsu is wrongly accused of a crime he didn't commit, like being framed for causing great harm to the guild. Another could be a dark magic influence. If some powerful dark magic gets into the guild members' minds, they might turn on Natsu without realizing it. Also, it could be a sacrifice situation where the guild believes sacrificing Natsu would save the rest of the world from a great evil.
A plot could be about a new guild master having to deal with a powerful dark guild threat. The new guild master, say someone like a new character introduced in the fanfiction, has to unite the Fairy Tail members, who are initially skeptical of their leadership. They have to come up with new strategies to combat the dark guild's unique magic and overcome internal differences within Fairy Tail.
He could leave because of a misunderstanding. Maybe he overhears something wrong and thinks the guild doesn't trust him or value him anymore. So in a fit of anger and pride, he decides to leave.