Fullmetal Alchemist Brotherhood is extremely close to the manga. It follows the story and characters very accurately, with few significant differences.
Fullmetal Alchemist: Brotherhood does indeed cover the whole manga. It follows the manga closely and presents all the major plot points and character developments.
Overall, Fullmetal Alchemist Brotherhood adheres closely to the manga. There are minor tweaks for the sake of animation and pacing, but the core story and characters remain largely intact.
If you're writing a Fullmetal Alchemist Brotherhood OC fanfiction, research is key. Dive deep into the lore of the series. Know about the different types of alchemy, like the forbidden alchemy. Your OC might be tempted by the power of forbidden alchemy, which could lead to an interesting plot. Another thing to consider is the cultural aspects. For instance, the Xingese culture plays a part in the story. Maybe your OC has some connection to Xing. You can also look at the power dynamics between the military and the civilians. Is your OC a part of the military? If so, what are their views on the military's actions? All these elements will add depth to your OC and make your fanfiction more immersive.
The story of Fullmetal Alchemist Brotherhood spans a considerable amount of time. It covers various events and character developments over multiple episodes.