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.
Some characters like Natsu might be initially suspicious. He's always been competitive with Sting, so he might think they have some ulterior motives. But characters like Lucy would probably be more welcoming. She's always open - minded and would see it as an opportunity to make new friends. Happy would also be curious and might follow them around to see what they're up to.
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.
For Lucy, you could develop her character by showing her growing more confident in her magic. Maybe she starts to experiment with new ways to summon her Celestial Spirits or combines their powers in unique ways. With Sting, you can explore his past more deeply. Show how his experiences as a Dragon Slayer have shaped his personality, and have him face some internal conflicts related to his power and identity. As for Rogue, you could develop his relationship with his shadow. Maybe he discovers new abilities within his shadow magic. Also, in the fanfiction, put them all in situations that force them to interact and grow together. For example, a mission where they have to protect a village from a powerful dark mage.
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 great fanfiction could be 'The Bond of Dragonslayers'. It really delves into the relationship between Rogue and Sting. It shows their growth as characters, their teamwork, and how they support each other. It also has some really cool action scenes that are true to the Fairy Tail spirit.
One common theme is friendship. Since they are both dragon slayers in Fairy Tail, their friendship is often explored, like how they support each other through tough times.
There is a fanfiction that I really like which is 'Sting and Rogue: A Magical Bond'. This one focuses on how their individual magic powers interact and how that affects their relationship. It shows how they grow both as individuals and as a pair. It also has some great descriptions of the Fairy Tail world, making it a really immersive read.