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.
An interesting OC for a Fullmetal Alchemist fanfiction could be a young alchemist prodigy. This OC could have mastered alchemy at a very young age due to a traumatic event that forced them to quickly learn self - defense through alchemy. They could enter the story by challenging Edward or Alphonse in an alchemic duel, believing they are the best. Or perhaps an OC who is a descendant of one of the great alchemists from the past, and they are on a quest to uncover secrets their ancestor left behind, which gets them involved with the main characters.
You could create an OC who is a journalist in the Fullmetal Alchemist world. Their goal is to expose the truth about the military's use of alchemy and the dark secrets behind it. They start investigating the Elric brothers' journey because they suspect there is more to it than meets the eye. This OC could add a different perspective to the story as they are not directly involved in alchemy but are affected by it. Also, an OC that has the ability to reverse alchemy, which is unheard of in the Fullmetal Alchemist universe, could be really interesting and cause a stir among the existing characters.
If you want the clearest chapter reference, go to Chapter 197. Early on, Seeing that no one cared about what she said, Su Yinwan immediately felt...; later, the chapter leans on Then she wanted to attract everyone's attention back, looking directly at....
Chapter 160 is the strongest chapter-level answer because it starts from As the sky gradually darkened, the originally mild drizzle began to... and follows through on Then came Shu Yan and Jiang Li, while He Yun silently moved to the back of....
The best chapter pointer here is Chapter 191, "Sister, Jiang Cheng is bullying me!". It opens with This change made Jiang Cheng extremely uncomfortable. and closes on Meanwhile, Jiang Shixu was staring intensely at the fragments on the floor..
Look to Chapter 192 for the clearest answer. It begins with Jiang Shixu had never imagined that Jiang Cheng, who had been so arrogant..., keeps building through On the other end of the phone, Jiang Li was also silent for a moment..., and lands on Jiang Li responded with a detached "hmm" from the.
The best chapter pointer here is Chapter 199, "You Found Out Long Ago?". It opens with Damn, the production team is actually being so generous this time, giving... and closes on You knew all along?" Zhao Lang adopted a contemplative look before curving....
Look to Chapter 195 for the clearest answer. It begins with Jiang Yan was fully equipped and followed at the end of the team., keeps building through He was wearing a sports suit borrowed from He Yun, his face smeared with..., and lands on The audience and fans would definitely think she was.
Chapter 191 is the strongest chapter-level answer because it starts from This change made Jiang Cheng extremely uncomfortable. and follows through on Meanwhile, Jiang Shixu was staring intensely at the fragments on the floor..
Chapter 192 is the strongest chapter-level answer because it starts from Jiang Shixu had never imagined that Jiang Cheng, who had been so arrogant... and follows through on Jiang Li responded with a detached "hmm" from the other end..
Look to Chapter 167 for the clearest answer. It begins with By the experimental field, Qi Tianyu was quite helpless as he watched Wen..., keeps building through He tried once again to pull back his suitcase, but to no avail, as one end..., and lands on Even when getting into the car, Qi Tianyu was.