One idea could be a crossover where Edward and Urahara meet in a world that combines their respective universes. They could exchange knowledge about alchemy and spiritual powers. For example, Edward could be intrigued by Urahara's zanpakuto and its unique abilities, while Urahara might be interested in the principles of alchemy.
Another idea is that they team up to face a common enemy. Maybe a powerful being that threatens both their worlds. Edward's combat skills along with his alchemy and Urahara's strategic mind and powerful spiritual techniques would make for an exciting partnership. They would have to learn to work together despite their different backgrounds and ways of doing things.
Perhaps Edward and Urahara would have an interesting dynamic in combat. Edward's quick - thinking and ability to transmute objects on the fly could be a great complement to Urahara's zanpakuto skills and his use of various spiritual items. They could learn from each other's fighting styles and develop new techniques together. Urahara might also introduce Edward to some of the other characters in the Bleach universe, like Orihime and Chad, and Edward could share stories about his friends in Amestris.
They could start by comparing their different worlds. Edward would explain about the principles of alchemy like equivalent exchange, while Urahara would talk about the Soul Society and the way spiritual power works. This exchange of knowledge could be the foundation for their relationship in the fanfiction.
In this fanfiction, her role as an alchemist might be perceived differently. As a girl, she might face more discrimination in the male - dominated field of alchemy. This could lead to stories of her having to prove herself more often and in different ways than in the original story.
Well, Edward's alchemy could be combined with Urahara's spiritual energy. For instance, Urahara could use his spiritual power to enhance Edward's alchemy transmutations. Or Edward could use his alchemy to create structures or tools that help Urahara in his battles against Hollows.
A crossover with the world of Attack on Titan could be interesting. Female Edward could use her alchemy to help in the fight against the Titans. Maybe she could create new weapons or defenses using her alchemical knowledge. And her relationship with the Survey Corps members would be a great source of character development.
A really interesting plot could be a time - travel scenario. Chimera Mustang and Edward Elric get sent back in time to a crucial point in the history of alchemy. They have to navigate this new - old world while also trying not to change history too much. This would be full of opportunities for them to interact with past versions of characters and maybe even prevent some future disasters.
One idea could be a story where Edward's friends throw him a surprise birthday party. They decorate the alchemy lab with streamers and balloons. Alphonse secretly bakes a cake with the help of Winry. Everyone gathers around as Edward walks in, completely shocked and overjoyed at the sight.
Well, perhaps in the fanfiction, Edward is kidnapped by a secret organization that wants to use his knowledge of the military's alchemical operations. They might hold him captive in an underground lair, filled with strange alchemical contraptions. Or maybe he's kidnapped by a jealous alchemist who feels overshadowed by Edward's fame. This alchemist could try to steal Edward's research and take credit for his work. Also, it could be that an otherworldly being kidnaps him to learn about human alchemy.
Well, a plot could involve Edward being betrayed by a mentor figure. This person could have been guiding him in alchemy all along but has a hidden agenda. Maybe they want to use Edward's unique alchemical abilities for their own dark experiments. Or, in a different scenario, Edward could be betrayed by a love interest. She might pretend to love him while actually spying on him for an opposing force, stealing his secrets and leaving him heartbroken and in a difficult situation.
Well, perhaps in the fanfiction, Edward's sacrifice causes a rift in the fabric of time. This rift then starts to distort reality, and it's up to his friends to figure out how to fix it. They have to journey through different time periods and face challenges that Edward had faced before. Or it could be that his sacrifice was misinterpreted by some, and they start to view alchemy as a dangerous art again, leading to a conflict between those who understand the true meaning of Edward's sacrifice and those who don't.