Friendship is a very common theme. Since they are both characters from the same universe, their friendship often forms the basis of many fanfics.
Common themes could include friendship, loyalty, and the development of a special bond between Erza and Mira.
Love and redemption are common themes. Given their past, Jellal has a lot to atone for, and in many fanfics, Erza's love becomes a part of his redemption journey. Another theme is the struggle between duty and personal feelings. They both have important roles in their world, and finding a balance between that and their relationship is often explored.
Another theme is adventure. Since they are from different realms, they usually embark on a journey together. This could involve exploring new places, facing unknown enemies, and uncovering secrets. In many fanfics, they use their unique skills to overcome obstacles during these adventures.
The fanfic 'Erza and Mira: United We Stand' is also worth checking out. It showcases how they work together as a team, relying on each other's skills. The author does a great job of creating a believable and engaging story around their relationship.
One common theme is the complex love triangle. Since all three characters have their own feelings and histories, the fanfics often explore how they deal with their emotions towards each other. Another theme could be their shared adventures and how their relationships develop during those experiences.
Friendship is a common theme. Often, the fem oc starts as a new acquaintance to Erza, and they build a strong bond of friendship that can withstand various challenges. For example, in many fanfics, they support each other during difficult guild missions.
Love and attraction are common themes. Since it's a ship - focused fanfic, the relationship between Erza and Gray is at the center. Another theme could be conflict, like internal conflict within themselves about their feelings or external conflict that tests their relationship.
One common theme is protection. The brother might be very protective of Erza Scarlet, given the dangerous situations they often face in the Fairy Tail universe. Another theme could be loyalty. They would be loyal to each other no matter what challenges come their way.
A common theme is friendship. Since Naruto and Erza come from different universes, their journey of becoming friends is often explored. For example, they might start off not trusting each other but then learn to rely on one another.
Another theme might be the growth of their relationship over time. Maybe at first they start off on a rocky or tense note, but as the story progresses, they come to understand and care for each other more deeply. There could also be themes related to the challenges they face together, whether it's external threats or internal struggles within their relationship.