One idea could be a new team emerging during the GMG with unique magical abilities that no one has seen before. They could bring a whole new dynamic to the competition.
Another plot could be that there is some sort of mystery or conspiracy behind the GMG. For example, an outside force is trying to manipulate the results for their own gain. A group of Fairy Tail members could uncover this plot and have to figure out how to expose it while still competing in the games. This would add a layer of intrigue and mystery to the story.
A plot could involve a powerful dark force threatening both the Naruto and Fairy Tail universes. This force could be something that neither ninjutsu nor magic can easily defeat. So, the characters from both worlds must come together. The GMG could be a platform where the first interactions occur. Maybe some Naruto characters enter the GMG under false pretenses to investigate this new threat that seems to be related to the event.
One idea could be creating an OC who has a unique magic related to the elements but in a very different way from the existing characters. For example, an OC that can manipulate the emotions associated with elements rather than the elements themselves. This could lead to some really interesting interactions during the GMG as they might be able to influence the performance of other competitors by affecting their emotional state related to their magic.
One idea could be a new character arriving at Fairy Hills and having to adapt to the unique living situation. They could face challenges like getting along with the different personalities of the Fairy Tail mages living there.
One way they could cross over is through a shared magical element. In Naruto, there are various jutsu which could be seen as a form of magic like in Fairy Tail. And the Grand Magic Games (GMG) in Fairy Tail has a tournament - like structure. So, perhaps a tournament could be set up where characters from Naruto and Fairy Tail participate. The Naruto characters could use their unique abilities like Sharingan or Rasengan, while Fairy Tail mages use their magic spells. This would create an interesting dynamic where different power systems interact.
Perhaps there's a dark secret hidden in the academy's history. A group of students accidentally stumbles upon it and has to work together to either keep it buried or expose it, depending on what they find out. Along the way, they face many obstacles and learn more about themselves and their magic.
A cool plot could be that a powerful artifact in Skyrim is causing chaos and the Fairy Tail members are summoned to find and secure it. Along the way, they meet up with the Dragonborn. Some members might befriend the Dragonborn and help in their battles, while others might be a bit more skeptical and think the Dragonborn is a threat to their own power within the group.
One idea could be that Ichigo arrives in the Fairy Tail world and his powerful spiritual energy is mistaken for a new type of magic. He could join forces with Natsu and the gang to fight against a common enemy that threatens both his world and the Fairy Tail world. Another could be that Ichigo's zanpakuto has some sort of unique interaction with the Fairy Tail magic, like being able to absorb or nullify certain spells.
One idea could be a story where a character from Fairy Tail is injured and ends up in a hospital in a foreign land. They meet a mysterious healer there who has a connection to an ancient Fairy Tail magic. Another could be that the hospital is actually a front for an evil organization that is stealing the magic of Fairy Tail members who come for treatment. Or perhaps a Fairy Tail mage has to use their magic in creative ways to heal the sick in a hospital that's short on supplies.
One idea could be Carla getting lost in a mysterious magical realm and the Fairy Tail members have to search for her. This could lead to new friendships and alliances as they explore the unknown area.
One idea could be to focus on an alternate origin story for a main character in Fairy Tail. For example, exploring how Natsu's past could have been different and how that would change his relationships in the guild.