Roy Mustang might also be paired with Edward in some fanfictions. They could be on a joint mission in the other world, with Mustang's strategic mind and Edward's combat skills combining to face the new threats. Their banter and the way they work together can be a great source of entertainment and plot development.
Winry Rockbell is often paired with Edward. Their relationship from the original series can be further explored in the alternate world setting. Maybe in this new world, they have different challenges in their relationship, like different social statuses or new enemies that target their relationship.
Alphonse Elric is often present. He might play a role in helping Edward understand and use his new gamer - like abilities in relation to alchemy. For example, he could be the one who discovers a new aspect of Edward's powers.
One interesting plot could be Edward trying to adapt to a world where alchemy doesn't exist in the same way. He might have to learn new forms of magic or technology to get by. For example, he could struggle with not having his alchemy skills to help him in combat or solve problems at first, but then gradually discovers new powers within himself in this new world.
Obviously, Edward Elric himself is the central character in this type of fanfiction. His brother Alphonse might also be a common character, often trying to help Edward deal with his new situation. Winry Rockbell could be there too, perhaps having a different kind of relationship with Edward now that he is a girl. There might also be the appearance of some of the villains from the original story, who could either take advantage of Edward's new form or be involved in the reason why he turned into a girl in the first place.
There's a chance that Scar could betray Edward in certain fanfiction concepts. Scar has his own motives and a complex past. If he feels that Edward is getting in the way of his revenge or his understanding of alchemy, he might betray him. Additionally, some fanfictions might explore the idea of an old acquaintance from Edward's childhood betraying him. Maybe someone who was once a friend but has since been corrupted by power or a dark influence. And then there's always the possibility of a new, mysterious character being introduced specifically to betray Edward for some yet - to - be - revealed reason.
Edward might meet his parents. Since he has the chance to go back in time, he could meet them when they were alive and perhaps learn more about alchemy from them, which could change his future actions.
Rukia could be a great character to pair with Ichigo. Since they have a strong bond in the original series, in the fanfiction, she could follow him into the other world or be summoned there later. Their combined power and friendship would make for an interesting dynamic as they face new challenges.
A common theme is the struggle against gender norms. Since Edward is male in the original, making him female in fanfiction often leads to stories about how she has to fight against the expectations placed on women in the world of alchemy. For example, she might face discrimination when trying to access certain alchemical knowledge or facilities.
One common theme is redemption. Edward often tries to make up for the wrongs done to the Ishvalans. Another theme is cultural exchange. Since they come from different backgrounds, there's a lot of learning about each other's cultures. For example, Edward might learn about Ishvalan traditions.
Another theme is the support system around him. In these fanfictions, his friends and family, like Alphonse and Winry, often rally around him. It emphasizes the importance of relationships in difficult times. For example, they might search for a cure or just be there to comfort him. This theme also helps to develop the other characters more deeply as they show their care for Edward.
Many 'immortal Edward Elric' fanfictions explore the idea of him being a lone figure in different historical periods. He might be a witness to great events, wars, and social changes. This gives the writer a chance to show how Edward's character and values from his original world interact with different historical and cultural contexts. Also, his relationship with his brother Alphonse could be a central theme, perhaps with Alphonse being reincarnated or Edward trying to find a way to bring him back in different ways throughout the centuries.