The alchemists' ability to transmute matter could be combined with Pride's shape - shifting abilities. For example, an alchemist could transmute a basic structure, and then Pride could use his powers to shape it into a more complex and efficient form. This would require a lot of cooperation between the characters, which could be interesting to write about.
Let's start with Naruto's ability to control the Nine - Tails' chakra. In a crossover, this could be related to the power of the Philosopher's Stone in Fullmetal Alchemist. Maybe the Nine - Tails' chakra has some alchemical properties that can be harnessed. Edward could study this and find a way to use it in his alchemy. On the other hand, the alchemical transmutation circles could be used as a form of jutsu in Naruto. The ninja could draw these circles on the ground or on their bodies to activate different powers. For example, Rock Lee, who doesn't have natural chakra control, could use alchemical transmutation to enhance his physical abilities. He could transmute his muscles to be stronger or more elastic. And for the Homunculi, they could use their immortality to outlast the ninja in long - term battles and learn their techniques over time.
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.
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 popular character is Scar. His unique brand of alchemy and his backstory of revenge can create some really intense crossovers. Edward Elric, as mentioned before, is always popular. He can be paired with characters from other series to have some amazing adventures. Hohenheim is also a character that shows up in a lot of crossovers. His long life and his connection to the Homunculus can add a lot of depth to crossover stories. He can interact with other powerful or long - lived characters from different universes in very engaging ways.
Well, consider Wendy's healing magic. In a crossover, she could use her magic to heal the wounds caused by alchemical experiments gone wrong or battles in the Fullmetal Alchemist world. In return, the alchemists could teach her about the properties of different herbs and substances that could enhance her healing magic. Gajeel's iron dragon slayer magic could interact with the metal - based alchemy. He could use his magic to shape and manipulate metal in ways that the alchemists find fascinating. And then there's Mirajane's transformation magic. She could transform into forms that are better suited to deal with the alchemical threats in the Fullmetal Alchemist world, while the alchemists could help her understand the physical and chemical changes that occur during her transformations.
Edward Elric from Fullmetal Alchemist would probably be very curious about the unique abilities in RWBY, like semblances. He might try to study them from an alchemical perspective. Ruby, on the other hand, would likely be in awe of Edward's alchemy skills and his mechanical arm and leg. She could see him as a kind of mentor in a way.
Some characters might be quite shocked or amused if they could read fanfiction about their own story. For example, Edward Elric would probably be very indignant at some of the out - of - character portrayals of himself. He's a proud alchemist and seeing himself depicted in a way that doesn't match his self - image would surely make him fume.
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 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.
A plot could involve the Avengers trying to understand the concept of alchemy. Maybe Tony Stark becomes really interested in it and tries to incorporate it into his tech. Meanwhile, the Fullmetal Alchemist characters are in awe of the high - tech world of the Avengers. They could end up sharing knowledge and skills to take on a powerful foe that neither could defeat alone. For example, a powerful demon from the Fullmetal Alchemist world that has found a way to use advanced weaponry from the Avengers' world.