One idea could be a crossover where Harry Potter characters end up in the world of Fullmetal Alchemist. For example, Harry could use his magic in Amestris and face the challenges there. Another could be a story where the alchemy principles are somehow introduced into the Hogwarts curriculum. And a third idea might be a fanfic where a character from Fullmetal Alchemist attends Hogwarts and has to adapt to the magical world.
Well, for a Harry Potter and Fullmetal Alchemist fanfiction, you could write about how the Philosopher's Stone in Harry Potter is related to the concept of the Philosopher's Stone in Fullmetal Alchemist. Maybe there's a way to combine the two universes' understanding of it. Also, a story about a character from Harry Potter using alchemy to solve a problem in their own world could be cool. Or perhaps a fanfic where the Homunculi from Fullmetal Alchemist invade Hogwarts and the students have to fight them using both magic and alchemy.
In some fanfictions, you could explore a scenario where the Deathly Hallows from Harry Potter have an equivalent in the Fullmetal Alchemist world. For instance, the Elder Wand could be compared to a powerful alchemical tool. You could also write a story where a character from Fullmetal Alchemist travels to the wizarding world and tries to learn magic, but has to overcome the differences in the two systems. Additionally, a plot where the magic of Harry Potter and the alchemy of Fullmetal Alchemist are combined to defeat a common enemy would make for an exciting fanfiction.
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?
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.
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.
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 idea could be a crossover where Naruto's chakra system somehow gets intertwined with Alchemy. For example, Naruto could learn to transmute his chakra into different elements in a more alchemical way rather than just using ninjutsu. Another could be that characters from both universes meet in a strange in - between dimension. Maybe Sasuke and Edward Elric could have an intense battle or a deep conversation about their quests for power and revenge. And perhaps Hinata could learn some alchemical self - defense techniques from Winry Rockbell.
Well, one interesting plot point is when the magic and alchemy clash. For example, in some fanfics, a wizard tries to use alchemical techniques and it backfires because the two systems are not fully compatible at first. It creates a lot of chaos and makes for an exciting read.
One plot idea could be Scar crossing over into a world where alchemy doesn't exist, and he has to adapt to a completely different form of combat and magic. Another is a crossover with a modern - day world, and Scar has to deal with modern technology and society while still holding onto his beliefs.
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 great Fullmetal Alchemist and Harry Potter fanfiction is 'The Alchemist's Wand'. In this story, the main character from Fullmetal Alchemist somehow gets transported to the Harry Potter world. It's really interesting to see how the alchemy concepts blend with the magic of Harry Potter. The author does a great job of maintaining the unique personalities of characters from both universes.