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.
Happy would be excited to have another dragon - related presence in the guild. He might see Igneel as a source of great stories and adventures. Gray, on the other hand, would be initially indifferent but as he sees the benefits Igneel brings to the guild, like new forms of magic training, he would start to respect him.
The characters in Fairy Tail would have a wide range of reactions. Makarov, as the guild master, would be very cautious. He would need to ensure that Acnologia's presence doesn't put the guild in more danger. Happy would be constantly on guard around Acnologia, ready to fly away at the first sign of trouble. The Thunder Legion would likely be in a state of high alert. However, some of the more adventurous members like Cana might see it as an opportunity for great adventures and powerful new magic. It would be a complex situation with different characters having different stances based on their personalities and past experiences.
Lucy could be extremely excited. After all, finding Igneel is like stumbling upon a legend come to life. She would likely be in awe of his presence. She might immediately think about how this discovery could benefit her friends in the Fairy Tail guild. She could also be very respectful and try to approach Igneel in a friendly manner.
The guild as a whole would likely mobilize. Erza would start formulating a strategic plan. She'd consider the strengths and weaknesses of Acnologia and figure out the best way to approach the situation. Gray would also be ready to fight, using his ice - make magic to support the rescue mission. They would all be united in their determination to get Lucy back safely.
The Fairy Tail guild would probably be very curious about Naruto at first. They might be amazed by his strange abilities like running up walls and creating clones. Some members, like Lucy, would likely be a bit cautious, but also intrigued. Natsu would probably be eager to test his strength against Naruto right away.
Fairy Tail would be a mix of reactions. The younger members would be thrilled and look up to Naruto as a hero. The older and more experienced members would assess his skills and how he could fit into the guild. They might also be a bit protective of their way of life in the guild at first, but as they get to know Naruto better, they would accept him as one of their own.
Some members might be initially cautious. Given her past as a powerful and somewhat feared being, they would be worried about her true intentions. For example, Gray might be on guard until he sees her actions are genuine.
The guild would likely be ecstatic. Gray would probably make some snarky comment about Natsu finally growing up, but deep down he'd be happy for his friend. Erza would be all for it and might start planning the wedding immediately, giving orders to everyone in the guild to help out.
If Sasuke joined a Fairy Tail guild in fanfiction, there would be a lot of drama. The other guild members would be initially suspicious of him because of his cold and brooding nature. But his skills would quickly earn him respect. He might have a hard time adjusting to the guild's more laid - back and friendly atmosphere compared to the ninja world. However, his determination to become stronger would fit right in with Fairy Tail's spirit.
Naruto would likely be very confused at first. He has a strong sense of belonging and has always fought for his place in his own ninja village, so being suddenly banished from the Fairy Tail guild would be a shock. He might try to plead his case and explain that he has done nothing wrong.
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.