Sasuke would also be a strong contender. His Sharingan gives him an edge in combat, and if he were to gain immortality and access to Fairy Tail magic, he could become an extremely powerful character. He could use his Sharingan to analyze and copy magic techniques, making him a very versatile fighter.
However, Zeref from Fairy Tail is already a very powerful immortal character. If he were to somehow gain access to chakra and ninjutsu from the Naruto world, he could be nearly unstoppable. His knowledge of dark magic combined with new ninja abilities would make him a terrifying force in this fanfiction fusion.
It could be Naruto if he combines his chakra powers with Fairy Tail magic. He has an enormous amount of chakra and his ability to learn new things quickly could make him a formidable force. He might be able to master powerful magic spells on top of his already strong ninjutsu.
It's really hard to say. On one hand, you have characters like Gildarts in Fairy Tail who can destroy mountains with his magic. But then in Naruto, there are characters like Kaguya who has god - like powers. If we consider the ability to adapt, Naruto himself could be very powerful in a Fairy Tail - Naruto crossover. His ability to quickly learn new techniques and his never - give - up attitude would make him a formidable force. He could potentially learn some basic magic in no time and combine it with his ninja skills.
It could be Naruto himself. With his already powerful ninjutsu and the potential to gain Fairy Tail magic, he would be extremely formidable. His ability to quickly learn new skills and his large chakra reserve, combined with something like Fairy Tail's celestial magic, would make him a force to be reckoned with.
Well, Erza is a very strong character in Fairy Tail. She has a vast array of armors and combat skills. However, in a crossover, Sasuke could be a real contender for the most powerful. His Sharingan gives him amazing abilities like predicting moves and copying techniques. And his Rinnegan in later arcs makes him even more formidable. But then again, characters like Gildarts from Fairy Tail are also extremely powerful with their unique magic. So it really depends on how the crossover is written and what abilities are emphasized.
It could be Naruto with the power of spiral energy. Imagine Naruto being able to infuse his chakra with spiral power. His already formidable ninjutsu like the Rasengan could become exponentially more powerful. He could also use the concept of 'drill' from Gurren Lagann to enhance his attacks, making him a force to be reckoned with.
But we also can't forget about Ichigo in his final form. He has the power of a Soul King and his combat skills are top - notch. If he were to enter the Fairy Tail world with all his power, he would be able to take on most threats with ease. It really depends on how the crossover is written and what kind of challenges are presented to each character.
It could be Makarov. His experience and extremely powerful magic could give him an edge. He has seen many battles and his Fairy Law is a very strong spell. In a situation like an Infinity War, his leadership and power would be crucial for the Fairy Tail guild.
Probably Natsu. Natsu has his own dragon - slayer magic which is already very strong. If he were to bond with a legendary Pokemon like Rayquaza, he could become almost unbeatable. Rayquaza's flying and powerful attack abilities, along with Natsu's fire - based attacks, would create a terrifying combination in battles.
It's really hard to say. Goku in his Super Saiyan Blue form has incredible power levels and combat abilities. But then again, Acnologia from Fairy Tail is an extremely powerful dragon. If he were to face Goku, his dragon - like abilities and powerful magic attacks could pose a real threat. However, Goku has the ability to keep getting stronger during a fight, so it could go either way.
It could be a character like Madara from Naruto. He has the Eternal Mangekyo Sharingan and all kinds of powerful jutsu at his disposal. He was able to fight on a large scale and cause a lot of destruction. In the Fairy Tail side, characters like Makarov might also be considered. He has a lot of experience and powerful magic. But in the end, it really depends on how the fanfic writer decides to balance the powers and abilities of all the characters in the crossover.
It's hard to say, but one could argue that a merge between Gildarts from Fairy Tail and Kakashi from Naruto would be extremely powerful. Gildarts has incredible magic power and combat skills, and Kakashi is a highly skilled ninja with the Sharingan. Their combined abilities in terms of combat strategy, magic, and ninjutsu would make them a force to be reckoned with.