One common theme could be friendship. They might explore how Shell and Eric became friends and the adventures they have together. For example, they could be on a quest in a fantasy world and their friendship is tested along the way.
You can try fanfiction platforms like Archive of Our Own (AO3). It has a large collection of various fanfictions, and you might be able to find some great Shell x Eric ones by simply using the search bar. Just type in 'Shell x Eric' and browse through the results.
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.
Friendship is a very common theme. Writers often explore how Eric and William become friends, support each other, and grow together.
One common theme is the exploration of forbidden love. Since Eric has a rather antagonistic role in the original story, the idea of him and Tris getting together goes against the norm. Another theme is redemption. Eric might be seen as trying to redeem himself in Tris's eyes. And there's also the theme of power dynamics as they both come from different positions of power within the factions.
Love and loyalty are common themes. Their relationship is often tested, but they remain loyal to each other in many stories. For example, in some fanfics, Sookie has to choose between Eric and her human friends, and her loyalty to Eric shines through.
Another common theme is growth. They might start as two individuals with different views but as the story progresses, they grow together, both personally and in their relationship. For example, in some fanfictions, they learn to communicate better with each other which helps them face challenges more effectively.
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.
Often, loyalty is a big theme. Eric and Ronald might be in situations where they have to prove their loyalty to each other. And sometimes, there are themes of adventure where they face challenges together and their relationship deepens as a result. For instance, they could be on a quest to save their town or something similar, and through that, their bond becomes stronger.
A common theme is the exploration of power dynamics. Since Eric is often portrayed as a powerful figure in the Divergent world, the fanfiction often shows how this affects his relationship with the reader. Another theme is loyalty, whether it's loyalty to the faction or to each other.
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.