There are fanfics where an alchemist travels to different dimensions using alchemy. In these stories, they encounter strange new worlds and alchemical practices that they have to adapt to. For example, in one such fanfic, the alchemist enters a world where alchemy is powered by emotions rather than the typical elements.
One idea could be a story about a young alchemist who discovers a hidden power within themselves while on a quest to find a rare ingredient. They could face many challenges and make new friends along the way.
One plot idea could be that Harry discovers a hidden alchemical library in Hogwarts that has been long forgotten. In this library, he finds ancient texts that lead him on a quest to create a powerful elixir that can heal any wound. Another idea is that Harry teams up with an alchemist from a different magical school to compete in an alchemical tournament against dark wizards who want to use alchemy for evil purposes.
One interesting sakura alchemist fanfiction could be about Sakura's journey to master a new and powerful alchemical technique. Maybe she discovers a long - lost alchemical recipe that has the power to heal any wound, and she has to face many challenges to fully understand and use it.
One interesting storyline could be Harry Potter discovers a hidden alchemist society within Hogwarts. He then learns ancient alchemical secrets that help him in his fight against Voldemort. For example, he might find a way to transmute substances to create powerful magical defenses.
One interesting fanfiction could be about Harry Potter somehow ending up in the Fullmetal Alchemist world and learning alchemy. He might use his magic in combination with alchemy in unique ways to solve problems.
Some fanfictions explore romantic relationships that were only hinted at in the original. For example, a story about Roy Mustang and Riza Hawkeye's relationship developing in a different way, perhaps with more challenges or a different timeline that tests their loyalty to each other.
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.
One idea could be that the main character is reborn as an alchemist with a unique ability that was never seen before in the Full Metal Alchemist world. For example, the ability to transmute emotions into physical forms. This could lead to a whole new set of adventures and challenges as they try to understand and control this power while also dealing with the existing threats in the FMA universe.
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.
The fanfic might also focus on the relationships between the characters in a more in - depth way. It could show the bond between the Elric brothers in a different light, perhaps under extreme pressure. It could also explore the relationships between the military characters and how they interact when pushed to their limits at the 'Breaking Point'.