I'm not sure if there is such a specific fanfic. Fanfic availability can vary greatly across different platforms. You might need to search on major fanfic websites like Archive of Our Own or Fanfiction.net.
Friendship is a major theme. Since they are both part of the Fairy Tail guild, their bond is explored, whether it's just a normal friendship or something deeper.
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.
One common theme could be friendship development. Despite their different anatomies, they might start as strangers and gradually become friends. Another theme could be adventure. They could go on an adventure together, facing various challenges and growing closer through the experiences.
You can try fanfiction.net. It has a large collection of various fanfics, including 'oc x erza' ones. Just use the search function and type in the relevant keywords.
I really like 'Erza and the Mysterious OC'. The story starts with Erza being intrigued by the oc who has some special powers or abilities. As the plot unfolds, they form a deep connection that is both emotional and based on mutual respect. There are also some really cool fight scenes in it, which makes it even more exciting to read.
The idea of two powerful female characters interacting in a fanfic is always appealing. In strong Lucy x Erza fanfics, we get to see them not only as individual powerhouses but also as a duo. They can learn from each other, like Lucy learning discipline from Erza and Erza learning to be more flexible from Lucy. This mutual growth aspect makes the fanfics very interesting.
There's also 'Lucy and Erza: A United Front'. In this fanfic, their powers combine in really interesting ways. It delves deep into their personalities, with Lucy's determination and Erza's strong leadership. The plot is well - developed and keeps you hooked from start to finish.
One popular 'erza x gray lemon fanfic' is 'Frost and Steel'. It has an interesting plot where their relationship unfolds in a unique way. The author does a great job of building the tension between them.