Another plot idea is to have Bradley cross over into a different fantasy world. Maybe a world where magic works completely differently from his own. He could team up with characters from that world, learn their magic system, and use it to his advantage. This would also lead to some interesting character development as he adapts to a new environment.
One idea could be to have Bradley cross over into a modern - day world. He'd be out of his element, dealing with things like technology and modern social norms. It could be funny to see his reaction to things like cell phones or cars.
A third idea is to have Bradley cross over into a world that is a post - apocalyptic version of his own. He could see how his actions in his original world have had an impact on this new world. It would be a chance for him to face the consequences of his actions and perhaps try to make amends. He could also use his skills as a fighter and leader to help the survivors in this new world.
One idea could be that Naruto characters somehow end up in the world of Fullmetal Alchemist. Maybe Naruto and Sasuke are chasing after a rogue ninja who uses some strange alchemy - like jutsu to open a portal to the other world. There, they have to learn about alchemy to find their way back home and in the process, they meet the Elric brothers and team up to fight against common enemies, like homunculi who are interested in the power of chakra.
To create a compelling Bradley in a crossover, you need to keep his core characteristics. His sense of duty and his military leadership skills should be emphasized. For example, if he crosses into a world of pirates, he could use his leadership to organize the pirates into a more efficient crew.
A plot could involve a crossover where Pride somehow gets trapped in a human body like the main characters in Fullmetal Alchemist. He has to adapt to human emotions and limitations while also dealing with the alchemists who are initially very suspicious of him. This would be a great opportunity to explore Pride's character in a different light and see how he copes with his new situation.
One idea could be the alchemist using gamer skills to unlock new alchemical formulas faster. For example, they might complete certain quests in a virtual - like world within the fanfiction to gain knowledge of rare alchemical combinations.
One plot idea could be an OC who is secretly searching for a way to reverse the effects of human transmutation without the use of the Philosopher's Stone. They could be an outcast in the alchemist community because of their unorthodox methods. Another idea is an OC who discovers a hidden alchemical society that has been operating in the shadows, with their own set of rules and secrets that could change the balance of power in the Fullmetal Alchemist world. A third plot idea could be an OC who has the ability to see the souls of those who have been affected by alchemy, and they use this ability to solve mysteries related to past alchemical experiments.
Another idea might be alternative endings. Fanfiction often plays with the concept of 'what if' things had gone differently. Maybe if Edward had not been able to regain his brother's body, how would he have coped and what new path would his life take?
Well, a great plot twist might be that the characters from Fairy Tail end up in the world of Fullmetal Alchemist and are mistaken for some sort of alchemical creations. They then have to prove that they are not and in the process, they discover that their magic has some strange effects on the alchemy in that world. For example, Gray's ice magic could freeze alchemical reactions in unexpected ways. Another plot twist could be that the Gate in Fullmetal Alchemist has a link to the Fairy Tail's Celestial Spirit World. So when someone tries to open the Gate, they accidentally open a portal to the Celestial Spirit World instead, and all kinds of chaos ensues as spirits and alchemists meet for the first time.
One interesting concept could be the combination of different alchemical abilities from various characters in different universes. For example, if a character from another anime with a unique power system crosses over into the Fullmetal Alchemist world, it could lead to new alchemical reactions and techniques. Another concept might be the exploration of how different cultures and moral codes interact. Characters from different fictional worlds might have different views on equivalent exchange, which could create some really thought - provoking scenarios. Also, the idea of crossovers can introduce new relationships between characters. Characters who have never met before might form alliances or rivalries based on their own goals and personalities.
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.
One idea could be an OC who is a foreign alchemist with a unique form of alchemy based on their homeland's culture. For example, an alchemist from a desert region who uses sand-based alchemy. Another could be an OC that has a special connection to the Homunculi, not as an enemy but as someone trying to understand and redeem them. Maybe an OC that was experimented on by the same people who created the Homunculi and has some shared traits.