Some of the more cautious members, like Erza, might be a bit wary at first. She would be concerned about how Igneel's presence might change the power dynamics within the guild and what his intentions truly are. But over time, as she sees his positive influence, she would likely warm up to him.
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.
Naruto would probably fit into the Fairy Tail guild quite well. He has a big heart and is always eager to make friends, which is a common trait in Fairy Tail. His loyalty would also be a great asset to the guild. He could be like the new, energetic member who is always ready for an adventure.
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.
Well, Naruto is known for his strong leadership skills and determination. If he were the guild master of Fairy Tail, he would probably bring a whole new energy to the guild. He'd likely encourage members to train harder and push their limits, just like he did with his own friends in Konoha. Also, his unique ninja abilities could inspire new types of magic in the Fairy Tail world.
The Goblin's Tail is a popular fantasy novel that many readers like. The Dark Guild refers to an organization whose purpose I'm not sure about because it may have different meanings in different storylines. However, people from the Dark Guild had appeared in many of the fairy's tail doujinshi novels, and these novels might have a protagonist.
The other members of Fairy Tail would likely be very excited. Natsu might be a bit clueless at first but would soon be happy for them. Lucy would probably be super excited and offer to help Levy with anything she needs. Erza would be more reserved in her excitement but would offer her protection. Gray would probably make some teasing remarks to Gajeel about becoming a father.
Naruto would likely change the guild's training regime. He'd focus on building physical strength as well as magical power. Since he's used to intense training himself, he'd push the members to be better. He might also introduce a system where members help each other more directly, like his team - based approach in Naruto.
They would be a very unique addition. The Rinnegan user would bring in powers that the Fairy Tail guild has never seen before. They could use their Rinnegan to sense danger from afar, much like some of the more perceptive mages in Fairy Tail. And their combat abilities would make them a strong asset in battles against other guilds or dark forces.
The guild would be in deep mourning. Elfman and Lisanna would be especially devastated as she is their sister. The guild's morale would take a huge hit. Mirajane was often a source of strength and stability for the younger members. Without her, there would be a sense of emptiness in the guild hall.