I'm not sure specifically about Sting x Rogue fanfiction without mpreg. You could try looking on popular fanfiction websites like Archive of Our Own. Search for 'Sting x Rogue' and then filter through the results to find the ones that don't involve mpreg.
One common theme could be their friendship and rivalry. They are both strong characters, and fanfictions often explore how they compete with each other in a healthy way and also how they support each other when facing common enemies.
One common theme is friendship development. Since they are all characters within the same universe, fanfictions often explore how their relationships grow from just being acquaintances to close friends or more. Another theme is adventure. They might go on quests together and face various challenges that test their bonds.
The theme of loyalty also frequently appears. They are loyal to each other and their guild. In some fanfics, this loyalty is put to the test, like when they have to choose between their guild and some greater good that involves the other. Also, adventure is a common theme. They go on quests together, facing all kinds of magical creatures and challenges along the way.
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.
Friendship is a very common theme. Writers often explore how the reader can be friends with both Sting and Rogue, and the unique bond they all share. For example, they might go on adventures together in the Fairy Tail world.
Power dynamics is also a theme. Given their different magic abilities, fanfics might explore how they balance their powers in a relationship. For example, Sting's light - based magic and Rogue's shadow - based magic could interact in interesting ways in a relationship, both in terms of combat and in their personal connection.
There are also some fanfiction groups on Facebook. These groups can be a good source as members often share their own works or ones they've come across. But be aware that the quality and quantity might not be as high as on the bigger fanfiction platforms. Also, make sure to follow the group rules when looking for or sharing fanfictions.
One place to look for such fanfiction is Archive of Our Own (AO3). There are often well - written stories that focus on the relationship between Sting, the reader, and Rogue in a non - sexual way. You can search using the relevant tags and filters to find the ones that suit your taste.
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.