Well, it could be chaos. Zeref's dark powers would likely disrupt the harmony of Fairy Tail at first. His presence might cause a lot of suspicion and fear among the guild members.
If Naruto joined Fairy Tail in a fanfiction, he'd probably make some really interesting friends. He has that determined and kind - hearted nature that would fit right in with the Fairy Tail crew. He might even teach some of the Fairy Tail mages his ninja techniques, and in return, learn about magic from them. It could lead to some epic team - up battles where his ninja abilities and Fairy Tail magic are combined to defeat powerful foes.
Well, he would probably bring his unique determination and growth mindset. Izuku is used to facing challenges and working hard to overcome them in his own world. In Fairy Tail, he could learn new magic and team up with the guild members for various quests. His never - give - up attitude would likely inspire the other wizards in Fairy Tail.
Well, in such a fanfiction scenario where Shirou joins Fairy Tail, he'd be exposed to a whole new world of magic. Shirou's used to his own kind of battles, but in Fairy Tail, magic is the norm. He could learn about different types of magic from the other guild members. His own skills could be seen as something quite special in this magical guild. He might also get into some friendly rivalries with the more combat - oriented members, which would be fun to read about.
Well, he might bring in a new level of power. His skills and knowledge could enhance the guild's capabilities in battles against strong foes. Also, his past relationship with some of the members, like Erza, would add a lot of interesting drama and character development within the fanfiction.
One possible plot twist could be that Zeref has an ulterior motive for joining. Maybe he wants to use the guild's resources to further his own dark plans.
Most of the Fairy Tail members would not take it well. Happy, Natsu's closest friend, would be extremely confused and sad. He'd follow Natsu around, trying to get him to come back to the guild. Makarov, the guild master, would see it as a huge threat to the guild's safety. He might send some of the stronger members to keep an eye on Natsu and Zeref. And the younger members like Wendy would look up to Natsu so much that they'd be very disappointed and scared for him, thinking that he's making a big mistake by joining Zeref.
Well, in such a fanfiction, Naruto might bring his unique ninja skills to Fairy Tail. His shadow clone jutsu could be used in creative ways during battles in the Fairy Tail world. Maybe he'd form an interesting bond with Natsu, sharing their love for a good fight and loyalty to their friends.
Well, it could be really exciting. Harry's magic from the wizarding world of Hogwarts would mix with the magic in Fairy Tail. Maybe he'd learn new types of magic, like Fairy Tail's unique elemental magic. And he could team up with Natsu and the others to take on powerful enemies. His knowledge of potions and spells might also come in handy during their adventures.
If godlike Naruto joins Fairy Tail, he would bring in his unique ninja skills. His Rasengan could be a very powerful attack in the Fairy Tail world. He might also teach the Fairy Tail members some of his ninja stealth and movement techniques, which could enhance their combat abilities.
If Naruto joined Fairy Tail, his powers would likely be a very interesting addition. His chakra-based abilities like the Rasengan could be a unique form of magic in the Fairy Tail universe. He might have to learn to control his chakra in a new way to fit with the magical rules there. Maybe he could combine his shadow clone jutsu with some Fairy Tail magic for some really cool combat moves.