A fun plot could be a genie who is actually a lost spirit from an ancient Fairy Tail era. The genie appears to the modern mages and offers them wishes in exchange for helping it find its place in the world again. Along the way, the mages learn about the forgotten history of their guild through the genie's memories.
One idea could be a genie who is bound to a Fairy Tail mage and causes chaos within the guild by granting wishes in unexpected ways. For example, a mage wishes for more power and the genie gives them a power that is difficult to control, leading to all sorts of comical and dangerous situations.
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 idea could be Metalicana's backstory before he was known in the Fairy Tail world. Maybe exploring his early days as a dragon, his first encounters with other dragons or magical creatures. Another plot could involve Metalicana having a secret mission that is related to the future of the dragon slayers in Fairy Tail. It could also be interesting to have a plot where Metalicana has to team up with some of the Fairy Tail members in a time - travel adventure to save the past and thus ensure the future of the guild.
Another plot could involve a dark mage in the Fairy Tail universe summoning Deathwing to gain power. But the summoning goes wrong and Deathwing is only partially summoned. This weakened Deathwing starts causing destruction while also being hunted by Fairy Tail. The guild then has to decide whether to try and fully summon him to send him back or find another way to deal with him.
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 Gojo, with his overpowered abilities, joins Fairy Tail and becomes a mentor figure to the younger wizards. He could teach them new ways to use their magic and help them in battles against powerful foes.
A plot could revolve around a conspiracy within the tournament organizers. They could be trying to manipulate the results for their own gain, and the Fairy Tail members have to figure it out while competing.
A plot could involve Mystogan's past coming back to haunt him. An old enemy from his homeland tracks him down in Fiore. This forces him to face his past mistakes and traumas. Alongside his Fairy Tail friends, he has to find a way to defeat this enemy and finally come to terms with his past.
One plot idea could be exploring Aquarius's past more in - depth. Maybe a story where we see her life before she became a Celestial Spirit. Another could be a story where Aquarius has to team up with an unlikely character from Fairy Tail to save the Spirit World.
Maybe there's a new member who has a secret gangster past. They joined Fairy Tail to start a new life, but their old gangster buddies come looking for them. This causes a lot of internal conflict within the guild as some members don't trust the new person, while others want to give them a chance to prove themselves and fight off the old gang.
One plot idea could be Ranma getting transported to the Fairy Tail world and having to learn magic. Another is a team - up where the characters from both series face a common enemy. Maybe a dark magic user who wants to use Ranma's unique curse for their own evil purposes.