One idea could be to explore the backstories of the dragons more in - depth. Maybe show how they came to be involved in the wars in the first place. For example, there could be an ancient prophecy that led to their conflict.
A really exciting plot could be about a group of Fairy Tail mages who get transported back in time to the era of the Dragon Wars. They have to survive in that dangerous time while also trying to find a way to prevent the wars from starting. Along the way, they learn about the old magic used by the dragons and form unexpected alliances with some of the dragon - like creatures.
A really interesting plot could be a time - travel scenario. A Fairy Tail wizard somehow ends up in the past of the Star Wars universe, during the Clone Wars perhaps. They could get involved in the conflict, befriend some of the Jedi or even help Anakin Skywalker avoid his fall to the dark side. In return, the Jedi could teach the wizard some new skills related to the Force. Or, a Star Wars character could be transported to the Fairy Tail world and has to adapt to the magic - based society. They could use their technological knowledge to help Fairy Tail in a time of crisis, like when facing a powerful dark guild.
A great plot idea could be that a powerful dark force is emerging that is draining the energy of all three worlds. The Naruto characters, Fairy Tail wizards, and Dragon Slayers must team up. They start by having a big meeting to share their knowledge and figure out a plan. Along the way, they have to overcome their differences in fighting styles and beliefs.
One idea could be to focus on a Celestial Dragon that has been banished from its own realm and ends up in the Fairy Tail world. It could form an unlikely bond with a Fairy Tail member and learn about friendship and loyalty. Another idea is to explore the origin of the Celestial Dragons in the context of the Fairy Tail universe and how they came to be associated with the Celestial Spirit magic. Maybe a young Celestial Dragon is being hunted, and the Fairy Tail guild decides to protect it, leading to an epic adventure.
One idea could be a fanfic where the Dragon Slayers have to team up to face a new, powerful dark dragon that is immune to their normal attacks. They would have to discover new powers within themselves.
One interesting idea could be the exploration of the unique bond between dragons in the Fairy Tail universe. Maybe it shows how their mating rituals are related to their magical powers. For example, the transfer of certain magical abilities during the mating process.
One interesting plot idea could be that the Dark Dragon Slayer has a hidden past related to Laxus. Maybe they were both part of a secret experiment by a dark guild long ago. As the story unfolds, they discover this connection and have to team up against the remnants of that guild who are now after them. Another idea is that the Dark Dragon Slayer initially starts as an enemy to Laxus but then realizes they have a common enemy in a powerful, evil dragon that threatens the Fairy Tail guild. So they put aside their differences to protect the guild and its members.
One idea could be exploring the backstory of the Dragon Cry in more detail. Maybe there was a hidden power within it that was known only to the first dragon who created it. Another could be a story where a new character discovers the Dragon Cry and has to learn how to control its power before the bad guys get their hands on it.
One plot idea could be Aquarius getting lost in the human world. She accidentally gets separated from the Celestial Spirit World and has to find her way back. Along the way, she teams up with some of the Fairy Tail members who are initially skeptical of her but then realize she's not as bad as they thought. Another idea is that Aquarius discovers a hidden power within herself that she didn't know she had. This power could be related to a long - lost magic that was once prevalent in the Celestial Spirit World. It could put her in danger as there are forces that want to control this power.
Another plot could revolve around the origin of Dragon Slayer magic. Maybe a long - lost scroll is found that reveals secrets about how the magic was first created and what its true purpose was. This could lead the Dragon Slayers on a quest to find out more about their powers and their connection to the dragons.
Maybe the fanfiction could focus on a dragon slayer who loses their powers but then discovers a new way to regain them. For example, they might have to go on a spiritual journey and face their inner demons. Along the way, they form new bonds with the members of Fairy Tail, which helps them in their quest.