Perhaps in the fanfiction, Lucy discovers that Rogue has a secret mission that involves her family. As they work together, Rogue begins to question his own motives due to Lucy's kind heart. This leads to a lot of internal conflict for Rogue and a growing relationship between them.
One idea could be that Lucy and Rogue are brought together by a powerful magic artifact. They have to team up to protect it from an evil force that wants to use it for destruction. Along the way, they start to understand each other's pasts and form a deep bond.
One idea could be a time - travel plot where Lucy, Rogue, and Sting are sent back in time to the founding of Fairy Tail. They have to navigate the early days of the guild while also trying to find a way back to their own time. Another could be a magic - swapping scenario, where they accidentally exchange their magical abilities and have to learn to use each other's magic to fight a new, powerful enemy.
A possible plot could involve a dark magic that starts affecting Fiore. Lucy discovers some ancient texts about it, and she realizes she needs the help of Sting and Rogue. They go on a journey to find the source of this dark magic. Along the way, they encounter many enemies. Sting and Rogue use their Dragon Slayer magic to fight, while Lucy summons her Celestial Spirits. As they get closer to the source, they find out that one of their old enemies has returned and is using this dark magic to seek revenge. Together, they combine their powers to defeat the enemy and save Fiore.
One idea could be a story where Sting and Rogue have to go on a special mission together in a new, uncharted land. They face various magical creatures and have to learn to trust each other even more. Another could be a fanfic set in an alternate universe where they are not part of Fairy Tail, but are instead traveling rogues who cross paths with characters from Fairy Tail in unexpected ways.
Perhaps there is a prophecy that only Rogue and Kagura together can fulfill. It could be about restoring a long - lost magical artifact that has the power to bring peace between their two warring lands. Along the way, they face opposition from those who want to use the artifact for evil. As they work towards the goal, they learn more about each other's cultures and values, and their bond grows stronger.
One idea could be Future Rogue trying to change the course of a major event in Fairy Tail's future. For example, preventing a powerful enemy from attacking the guild. He could use his knowledge of the future to his advantage.
Maybe a plot where Yukino gets kidnapped by an enemy, and Rogue has to go through a series of trials to rescue her. During this, he discovers new aspects of his own power and his feelings for Yukino. It could involve a lot of action scenes as Rogue battles the kidnappers and their minions. Also, there could be some emotional moments when he finally reaches Yukino and they share a tender moment.
One idea could be that Lucy and Angel are forced to team up against a common enemy stronger than them. They start off distrusting each other because of their past differences. But as they fight side by side, they begin to understand and respect one another's powers and personalities.
One idea could be a story where Lucy and Erza have to team up to save the Fairy Tail guild from a powerful dark magic that's slowly corrupting it. They'd face many challenges and have to rely on each other's unique magic abilities. Another could be a time - travel plot where they go back in time and meet the founders of Fairy Tail and learn some long - lost magic techniques. Maybe they also have to change a certain event in the past to save the future of the guild.
Maybe a plot where Lucy and Yukino accidentally switch magical powers. This leads to a series of comical and also dangerous situations. They have to figure out how to reverse it while also dealing with enemies who want to take advantage of their confusion.
One idea could be that Lucy discovers she has hidden witch powers passed down through her family. Maybe she can use these powers to save the Fairy Tail guild from a new, powerful dark magic threat. Another plot could involve Lucy being transported to a parallel world where she is a well - known and feared witch, and she has to find her way back while also learning about her new - found powers in that world.