One great 'Fullmetal Alchemist Scar Crossover Fanfic' is 'Scar's New Path'. It takes Scar on an adventure where he teams up with characters from another universe. The story is really engaging as it delves into Scar's character development in this new and strange setting.
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.
One idea could be that Naruto somehow ends up in the world of Fullmetal Alchemist and his chakra-based attacks are mistaken for some form of alchemical explosions. For example, his Rasengan could be seen as a condensed form of alchemical energy that explodes on impact.
One interesting fanfic could be where the alchemist characters find themselves in the wizarding world of Harry Potter. They might use their alchemy skills in Hogwarts, which could create some really unique scenarios. For example, Edward Elric could try to analyze the magical properties of potions using his alchemical knowledge.
A good 'Fullmetal Alchemist Scar Crossover Fanfic' should first of all stay true to Scar's character. His backstory, his beliefs and his unique abilities should be respected. For example, if he's made to be too out - of - character, like suddenly being overly friendly without a proper reason, it won't feel right.
Itachi and Roy Mustang would be an interesting duo. Itachi, with his complex past and powerful abilities, and Roy Mustang, with his ambition and strategic mind. They could share their knowledge of different forms of combat and power manipulation. Itachi might be intrigued by Mustang's use of alchemy for combat, and Mustang could be interested in Itachi's Sharingan abilities and how they can be used in battle.
There probably are. Fanfiction writers often love to mash up different universes. In such a fanfic, Naruto could bring his chakra - based powers and blend them with the principles of alchemy from Fullmetal Alchemist. Maybe he'd use his Rasengan in a new way by incorporating alchemical transmutation circles. It would be a wild and creative concept.
One possible storyline is a cross - over where the ninjas in Naruto are exposed to the equivalent exchange principle of alchemy. They might start using it in their training, like instead of just relying on chakra, they think about what they are giving up to gain a new skill. For instance, a ninja might give up some of his speed to gain more strength. In the case of the Fullmetal Alchemist characters in the Naruto world, they could be involved in the battles between the villages. Alphonse could use his armor body to protect the villagers from attacks. And Scar from Fullmetal Alchemist could have an interesting interaction with the shinobi, as his unique form of alchemy might be seen as a very different type of jutsu.
One interesting concept could be the alchemy - ninjutsu fusion. Imagine Naruto characters using alchemical principles in their jutsu, like transmuting elements in a more alchemical way. Another concept might be the exchange of knowledge between the two worlds. For example, the alchemists teaching the ninja about equivalent exchange in combat strategies.
The characters' abilities can interact in really cool ways. For instance, Naruto's Shadow Clone Jutsu could be used in alchemical experiments. He could send clones to gather materials or perform different steps of an alchemical process simultaneously. In return, Edward's alchemy could be used to create structures that are useful for ninja battles, like creating instant fortifications or traps.