In a crossover with 'Naruto', Naruto himself would be a great character to pair with Natsu. They both have strong personalities and are determined to protect their friends. They could learn from each other's fighting styles, with Naruto showing Natsu some of his ninja techniques and Natsu teaching Naruto about magic.
Pairing Natsu with Asuna from 'Sword Art Online' could also be great. Asuna is a skilled fighter in the virtual world, and Natsu could bring his real - world magic to the mix. They could fight together against threats in a world that combines elements of the virtual and the magical, perhaps a virus in a game world that is spreading into the real world.
If it's a crossover with 'Fullmetal Alchemist', Edward Elric would be an interesting partner for Natsu. Edward's scientific approach to alchemy could contrast with Natsu's more instinctive use of magic. They could work together to solve problems in a world that combines the rules of alchemy and magic.
Goku from Dragon Ball Z could be a great crossover character for Natsu. They are both very strong and have a love for fighting. Goku's ki - based attacks and Natsu's fire magic would make for some epic battles. They could also train together and learn from each other's fighting styles. Also, Alucard from Hellsing could be an interesting crossover. His vampiric powers against Natsu's magic would create a very dark and intense story.
Gray would be a great character to pair with them. Gray has a long - standing relationship with Natsu, and his ice magic contrasts well with both Natsu's fire and Juvia's water. Their interactions can add a lot of humor and depth to the story, like Gray constantly arguing with Natsu while also trying to work together with Juvia.
Erza is frequently paired with Natsu in these fanfictions. Given her strong and leadership - like qualities, she can take charge in agent - related situations, and Natsu can be the more impulsive force. Their interactions can range from Erza scolding Natsu for his reckless actions to them having deep conversations about their responsibilities as agents. Wendy is also a character that can be paired with Natsu. Her healing magic can be crucial during dangerous agent missions, and she looks up to Natsu, which can create a sweet and protective relationship in the fanfiction.
A crossover with a superhero universe, say the Marvel universe, would also be exciting. Picture Natsu teaming up with the likes of Iron Man or Thor. Natsu's fiery nature might clash or blend well with the high - tech and super - powered heroes. He could help fight against villains like Thanos, using his unique brand of magic.
A fanfiction idea could be that in a crossover, Natsu is tired because he's been on a long - term mission in a different realm. He returns to Fairy Tail not quite himself. The guild members start to worry as he doesn't have his usual energy for pranks or challenges. As the story progresses, he slowly regains his strength through the support of his friends and the familiar environment of the guild, and in the end, he's back to his old self ready for new adventures.
Lucy could be a main character. She was always close to Natsu in the original Fairy Tail. So when Natsu returns as an 'ex' and meets the guild again, she would likely play a big role in how he is received and in the development of the story.
Gray would be one of the main characters to interact with Natsu. Their friendly rivalry is well - known in Fairy Tail. Makarov, as the guild master, would also have an important role in interacting with Natsu. He might give Natsu some important tasks or just have a grandfatherly chat with him about his return.
Gray would also be important. There could be a rivalry - turned - friendship aspect where Gray, who has his own ice - making powers, and Natsu, as a dragon, have to learn to work together. Maybe they compete in a friendly way to see whose powers are more useful in different situations.
Lucy is often paired with Natsu in many fanfictions. Their relationship can be explored in different ways in these fan - created stories. It could be a more romantic relationship than in the original series, or they could have a different kind of partnership, like being more equal in power or having different goals they pursue together.
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.