There could be a fanfiction where Sting and Rogue are challenged by a powerful dark wizard who wants to steal their dragon slayer magic. They have to team up not only with each other but also with other Fairy Tail members they don't usually get along with. This could lead to character development as they learn to work in a team outside of their usual duo and also explore the depths of their loyalty to the guild.
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.
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.
One idea could be that Sting and Rogue initially come to Fairy Tail as spies for Sabertooth, but as they interact with the Fairy Tail members, they start to question their loyalty to their old guild. They could be paired up with different Fairy Tail mages on missions. For example, Sting with Natsu and Rogue with Gray. Through these experiences, they see the true meaning of friendship in Fairy Tail which is different from the competitive environment in Sabertooth.
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 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 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.
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 a story where a rogue mage from a different guild infiltrates the Fairy Tail guild and causes chaos among the members. They could be stealing important artifacts or trying to disrupt the relationships within the guild.
Another common theme is power and growth. Writers often show how Rogue and Sting become stronger over time. For example, they might face a powerful enemy and through that experience, they learn new magic or improve their existing skills. It's about their journey to become more powerful dragonslayers.
Friendship is a very common theme. Sting and Rogue are often depicted as having a deep and unbreakable friendship. Another theme is adventure. They go on various adventures together in many fanfictions. And of course, the theme of magic is always there as they are part of the Fairy Tail world which is full of magic.