Luffy might befriend Erza. Erza is a strong and respected figure in Fairy Tail. Luffy respects strength, and Erza's no - nonsense attitude combined with her powerful combat skills would catch his attention. Once Luffy realizes that Erza also has a soft side and cares deeply for her friends, he would definitely want to be her friend. And Erza, seeing Luffy's pure heart and determination, would probably welcome him as a friend too.
I think Luffy would befriend Lucy first. Lucy is kind - hearted and she has a similar sense of adventure as Luffy. She also has a collection of celestial spirits which would be really interesting for Luffy. He might see her as a valuable ally and friend right away. And with Lucy being one of the more approachable members in Fairy Tail, it's likely that they'd start a conversation and become friends quickly.
Most likely he would befriend Natsu. They are both really headstrong and passionate about their respective skills. Natsu would be intrigued by Naruto's ninja abilities and Naruto would be interested in Natsu's fire - dragon - slayer magic. They would probably start off by challenging each other to a friendly fight and from there develop a bond of mutual respect.
Well, he might start challenging the Fairy Tail wizards to friendly battles. Since Luffy is all about adventure and getting stronger, he'd see the powerful mages in Fairy Tail as great opponents to test his skills against.
Another possible friend for Danny could be Hermione Granger. Hermione is always interested in learning new things. Danny's powers would be a fascinating subject for her to study. She might try to find a way to explain his powers through magic or Muggle science. And Danny could benefit from Hermione's vast knowledge of magic and Hogwarts.
Happy might also become Luffy's friend. Luffy would be amused by Happy's flying ability and his cute appearance. Happy could also help Luffy navigate the Fairy Tail world, as he knows it well. And Luffy might share his food with Happy, which would make Happy very happy indeed.
He would probably befriend the hobbits. The hobbits are friendly and curious, and Naruto's energetic and kind - hearted nature would attract them. They could learn a lot from each other, like the hobbits could teach Naruto about their simple but fulfilling way of life.
Makarov could be a great teacher. He has a wealth of knowledge and experience in magic. He could teach advanced magic techniques and also lessons about leadership and guild values. He would be strict but also very understanding and always ready to give good advice to the students.
One common theme is friendship. Just like in both the original series, fanfictions often explore the strong bonds between characters from One Piece (Luffy's series) and Fairy Tail. They show how characters from different universes can come together and support each other through tough times.
One challenge Naruto might face is getting used to magic. Since he's used to chakra - based powers, the concept and use of magic could be quite confusing at first. Also, the rules and culture of Fairy Tail might be different from what he's used to in Konoha. He'd need to adapt to the guild's way of doing things.
Probably Natasha Romanoff. Natasha is used to dealing with people who have a bit of an edge and a mysterious past, which Skye has. Natasha would be intrigued by Skye's skills and would likely reach out to her first.
She might befriend Iron Man first. Since he's into technology and Marinette is quite creative when it comes to making things. They could bond over creating new gadgets or improving existing ones.