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, the reactions would be diverse. Elfman would likely see it as a very unmanly thing to do at first. He'd be all ready to fight Natsu to bring him back to the right path. Cana would probably be more interested in what this new development could mean for the future of magic. She might be a bit more accepting than others, but still be cautious. Levy would be concerned about the knowledge that Zeref might expose Natsu to. She'd worry that it could change Natsu in a negative way and she'd try to research ways to break their alliance if possible.
The older members of Fairy Tail, like Makarov, would likely be very cautious. He has the responsibility of protecting the guild and its members. So, he would keep a close eye on Minerva. The younger members might be a bit more star - struck at first, seeing her as a powerful mage. But as they interact more, their reactions would depend on how Minerva behaves. If she's kind and helpful, they'll accept her, but if she shows any signs of her old ways, there would be problems.
Some of the more mischievous guild members like Gray might tease them a lot. He'd probably make jokes about it every chance he gets, much to Natsu and Lucy's annoyance. Happy, on the other hand, might be really confused at first but then start to see it as a sign of their closeness and be really happy for them.
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.
Some members might be sad at first. Lucy, for example, would surely miss him a great deal as they are close friends. She might worry about him constantly during his absence.
Gray would probably be one of the first to want to go after Natsu. He and Natsu have a long - standing rivalry but also a deep friendship. He'd be furious and determined to rescue Natsu. Lucy would be very worried too. She might use her celestial spirit magic to try and find Natsu's location. Erza would be very focused and strategic, rallying the rest of Fairy Tail to come up with a rescue plan.
The guild members' reactions would vary greatly. Happy, being Natsu's closest companion, would likely be excited about the fanfiction. He might fly around the guild hall, telling everyone about it and adding his own little comments about how accurate or inaccurate it is. He would definitely be protective of Natsu's image in the fanfiction, especially if it's not a positive portrayal.
Gray would be shocked at first. He and Natsu have a long - standing rivalry - but also a deep friendship. He might initially be angry that Natsu would just leave like that, but then he would realize how much he'll miss him. He might also feel a sense of loss for the guild as a whole, since Natsu is such an important part of it.
Well, it depends on the specific fanfiction. Some fanfictions do make Zeref and Natsu brothers. This can create some really cool plot twists. For instance, it could change how Natsu views his powers if he discovers he's related to Zeref. And it might also make Zeref more protective or possessive of Natsu in a different way than in the original story. It's a concept that allows for a lot of creativity in the fanfiction world.
Lucy would be extremely distraught. She and Natsu have a very close bond. She might cry for days and even isolate herself from the rest of the guild at first. Gray would be angry and feel a strong sense of loss. He'd probably blame himself for not being there to help. Erza would be stoic on the outside but inside, she'd be deeply affected. She'd take charge of the situation, making sure Natsu's death was not in vain and that the guild stays strong.
Natsu would be heartbroken. Fairy Tail is like his family. He'd probably go on a solo journey to clear his name and prove his loyalty. Erza would be stoic but deeply hurt. She'd start an investigation within the guild, using her influence and intelligence to uncover the truth. She might also isolate herself a bit while she figures things out.