Another plot idea is that an enemy from another dimension steals the Omnitrix and uses it to create havoc in the Fairy Tail world. The Fairy Tail members then have to track down the enemy and figure out how to defeat them without fully understanding the capabilities of the alien forms. They might have to rely on their own magic and teamwork to outwit the enemy who has the advantage of the Omnitrix powers.
One idea could be that a character from Fairy Tail finds the Omnitrix and has to learn how to use it without getting overwhelmed by its powers. Maybe they initially use it for simple tasks like getting out of tight spots during a guild mission, but as they get more proficient, they start using it in more complex battles against powerful foes.
A cool plot could involve the Omnitrix malfunctioning in the Fairy Tail world. It starts randomly changing the wearer into different alien forms at inopportune times. This causes chaos within the guild as they try to figure out how to fix it while also dealing with the strange situations the malfunctioning device creates, like an alien form that scares away all the local wildlife during a camping trip for a mission.
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.
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 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.
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.
In a 'Fairy Tail WW2 Fanfiction', a possible plot could be that the guild discovers a hidden magical dimension that is somehow connected to the events of WW2. They enter this dimension to try and stop a dark force that is influencing the war from the shadows. Some of the characters could form alliances with real - life military personnel who are open - minded enough to accept their help. This would lead to interesting interactions between the magical and non - magical worlds during the war.
Maybe a new character arrives at Fairy Tail who is a master chef. They create a special line of cheeseburgers that are enchanted. These cheeseburgers can heal minor wounds. The story could revolve around the guild protecting this chef and their magical cheeseburger recipe from villains who want to use it for evil.