Love is a very likely theme. In many fanfictions, the relationship between the two characters can evolve into a romantic one. This could be a slow - burn type of love where they start off as adversaries but gradually fall for each other. Additionally, themes of loyalty might be present. They might have to show loyalty to each other in the face of difficulties or against other characters in the reaper world.
I'm not sure about specific 'eric x alan bully reapers fanfiction' stories offhand. You could try searching on fanfiction platforms like Archive of Our Own. They have a vast collection of fan - created works and you might be able to find what you're looking for there.
One common theme might be the power dynamic. Since it involves a bully aspect, there could be a play on who has the power in the relationship between Eric and Alan. Another could be redemption. Maybe the bully (whichever character that might be) has a change of heart over time.
Friendship is often a common theme. The stories might explore how Eric and Alan's relationship develops from being just acquaintances to really close friends. Maybe they go through some challenges together that strengthen their bond.
Another theme could be self - discovery. As they interact, both Alan and Eric learn more about themselves, their strengths, and their weaknesses. This can be really interesting as it adds depth to their characters in the fanfiction.
One common theme could be friendship. Their relationship might be explored in terms of how they support each other through different challenges. Another theme could be adventure, where they go on some exciting journey together.
I'm not sure specifically about Eric Slingby x Alan Humphries bully fanfiction. Fanfiction can be a very niche area, and it might be difficult to find. You could try searching on dedicated fanfiction websites like Archive of Our Own and see if there are any works that match this pairing and theme.
One common theme could be friendship development. They might start as acquaintances and gradually become closer friends or more. Another theme could be adventure, where they go on some sort of journey together.
Duty is a big theme too. They have their duties in the Black Butler world, and fanfictions often play with how they balance their personal feelings with their duties. There's also the theme of mystery. Given the nature of the Black Butler universe, many fanfictions add more mystery to their characters, like uncovering secrets about their families or pasts that add more depth to their relationship.
Another theme is self - discovery. As they interact with each other, both Manon and Alan learn more about themselves. This is shown in stories where they have to face their own fears and insecurities while being with the other.
Another theme is growth. Both Ash and Alan are characters who can develop a great deal. In fanfiction, we often see them grow as trainers, as people, and in their relationship. They might learn from their mistakes, become more confident, and their relationship might evolve from just friends to something more meaningful over time.