Why Roy Mustang's Power In Fullmetal Alchemist: Brotherhood Is More Terrifying Than You Think
Roy Mustang is the cocky yet reliable flame alchemist who serves as one of the principal characters of the Fullmetal Alchemist franchise. He appears in all adaptations of the intellectual property, including the original manga, both anime, and the live-action movie. No matter the version, Roy serves as the superior officer to protagonist Edward Elric, the eponymous Fullmetal Alchemist. On top of that, he's one of the most powerful alchemists in the series, and one of the only ones capable of using his signature style, flame alchemy.
The end result of flame alchemy is fairly self-explanatory. Like other alchemists, Roy manipulates the laws of nature. Except, instead of manipulating stone or water, he creates fire. Whether it be streams of precise flame or massive explosions, Roy Mustang can make it happen with just a snap (though he isn't actually snapping) of his fingers. Here's the thing, though: Roy's alchemy is terrifying. This is true not just because he can make any man look like the aftermath of a bad barbecue without a second thought but because of how he manipulates fire.
How does Roy Mustang's flame alchemy work?
According to a breakdown made by YouTuber Sage's Rain, Roy Mustang creates fire through two key tools. First, there are his specially made ignition gloves, which allow him to create sparks. Second are the alchemist's transmutation circles sewn into the backs of said gloves. Using these tools, Roy can manipulate the density of the oxygen in the air to the point of ignition. This is what creates the "snap" effect whenever he creates fire, not the actual snap of his fingers.
Oddly, each glove has a slightly different purpose. One glove is specially geared toward creating large-scale explosions, while the other is built for manipulating fire in a more precise manner. Using these two together, Roy can use fire in almost any situation, though high humidity and rain make such things more difficult. Still, Roy has shown that he can overcome these environmental conditions through the use of a lighter and the manipulation of the oxygen in water. In truth, however, Roy could be much more powerful because oxygen manipulation has so many other applications.
Why oxygen manipulation is broken
Manipulating oxygen to create fire is, by itself, an incredibly powerful and versatile ability to possess. However, should Roy Mustang ever open his mind to all the applications having control over oxygen density has, he could become even more powerful. Imagine doing the reverse of what Roy tends to do and actually decreasing the overall oxygen density in a given space. Roy could make the air inside someone's lungs completely unbreathable. He could (as he once did with water) separate the oxygen from their bloodstream, rendering it useless.
Even if he only stuck to increasing the density of oxygen in a given space, Roy could do so much more. He could create an oxygen bubble inside someone's bloodstream large enough to cause a heart attack or a stroke, also known as an air embolism (via Healthline). With a flick of his wrist, he could end pretty much anyone's life without giving them any burn damage whatsoever. It's a scary power that has equal potential for covert and overt destruction should it fall into the hands of someone with a flexible imagination.