Their relationship could develop through mutual respect. If they are constantly thrown into situations where they have to rely on each other's skills. For example, in a battle against a powerful alchemist, Lust's combat abilities and Edward's alchemical knowledge could complement each other, leading to a grudging respect that might grow into a friendship of sorts.
One interesting plot idea could be that Edward and Lust are forced to team up against a common enemy. Maybe a new alchemic experiment gone wrong has created a powerful and dangerous being that threatens the world they know. Their combined knowledge of alchemy and Lust's unique abilities might make for an interesting dynamic as they struggle to defeat this foe.
One possible fanfiction could be about Edward and Roy teaming up for a dangerous mission. Maybe they have to infiltrate an enemy stronghold where they discover a new type of alchemy that they've never seen before. Along the way, they start to understand each other better and respect the other's skills.
One idea could be exploring Lust's backstory before she became a Homunculus. Maybe she had a human life before and what led to her transformation. Another could be a fanfiction where Lust forms an unlikely alliance with a human alchemist. They could work together to achieve a common goal, like saving a town from a greater evil.
Well, in fanfiction, Edward and Roy's dynamic can be really interesting. They have different personalities. Edward is young and impulsive, while Roy is more reserved and calculating. This contrast can lead to some really engaging storylines in fanfiction, like when they work together on a mission and Edward's quick actions either save or almost ruin the plan.
Maybe Edward dies in a fight against a powerful new enemy. This enemy could be someone who has mastered a dark form of alchemy that Edward couldn't counter. His death could then inspire the other characters, like Winry, to take up arms in a different way. She might use her skills as an automail engineer to create weapons that can defeat this new threat, all while mourning Edward and vowing to make his death count.
One common theme is redemption. Since they've both made mistakes in their alchemical pursuits, fanfictions often explore how they try to make up for those mistakes in different scenarios.
One common theme is identity. Since Edward is a male in the original, making him female in fanfiction often leads to exploring how this change affects his self - identity. Another theme is relationships. It could be how his relationships with other characters like Alphonse, Winry, or Roy Mustang are different because of the gender change. For example, a female Edward might have a different dynamic with Winry in terms of friendship or rivalry.
Often, fanfiction writers focus on the character growth that can occur through their interactions. Edward, who starts off as a headstrong and somewhat naive alchemist, can learn a great deal from Roy's strategic thinking. Roy, in turn, might be inspired by Edward's unwavering belief in doing what's right, regardless of the consequences. Their relationship could also be a source of conflict, as their personalities and goals don't always align.
If Edward dies, it would have a huge impact on Alphonse. Alphonse has always relied on Edward, and without him, he would be lost at first. But this could also be a turning point for Alphonse to become more independent and find his own path in life. He might start to question the things they've been doing in their search for the Philosopher's Stone and find a new purpose.