Ashes in the Air: On the theory and application of gaseous alchemy in uncontrolled environments.
A sort-of canon-plausibleish light AU.
In Riza's memory, her father had always been obsessed with air.
Alchemizing solids is the easiest. An alchemist, unless they are trying to alchemize while jumping, always has a rooted connection to the ground and the strain of tectonic energy therein. Channeling that into another solid that has a physical connection to ground or alchemist is essentially trivial. Skill in that form of alchemy comes from increasingly precise incorporation of intent, through which the alchemist controls not just the material composition of the transformation but the shape and form of the output, or in maintaining the connection as the material loses its grounding if thrown or launched.
Liquids are similar. They are trickier than solids as the molecules are no longer locked into a rigid structure. Liquids must be contained in something, so the alchemist can still maintain a direct grounding for the energy transfer through the contact of vessel to ground or alchemist and of liquid pressed against walls of the vessel. Controlling the form is harder than with sold material as a liquid's natural state can't independently maintain a form, so the alchemist must constantly direct energy towards the desired form.
But gasses are the hardest of all. There is so much space between molecules and so much motion that there is barely any direct grounding for the energy transfer. And even if the alchemist establishes a connection for energy transfer, it is confoundingly tricky to control the form when the molecules want nothing more than to fly every which way instead.
What little gaseous alchemy existed usually relied on enclosed gasses. Introduce a vacuum into a chamber, then fill it with a preferred gas mixture to a known density and pressure. Then do the math to approximate how many molecules are contact with the chamber wall at any given time, increasing the pressure to increase the contact, which creates a known basis to establish the grounding for the energy transfer. It then becomes possible to alchemically transform the gas within the chamber, with the option to transmute the chamber to vent the gas while maintaining the connection necessary to force intent upon it. However, to do that, the few alchemists who pursued gaseous alchemical research always did it in an enclosed room where they controlled the environment. They measured the composition of the air, the temperature, the humidity, the barometric pressure, eliminate drafts, control any pressure differentials, keeping all variables known and accounted for.
Her father had started with that. When she was younger, and her mother was still alive, and her father was kinder, Riza would follow him to his hermetically sealed room in the basement, where air was only introduced and vented by a cutting-edge HVAC system, the likes of which could otherwise only be found at a few premier universities. He'd draw a careful circle, place a pressure vessel on top, fill it from gas canisters, add colored smoke, then activate the circle and vent it from the vessel into the room as he shaped it into twisting, looping swirls above her head to her delight. All the while he would lecture on what he was doing, what new techniques he was trying, what hypotheses he had proposed, what questions were answered, and which remained. Not that he was explaining anything to her, specifically. More like he was composing his notes out loud, so he'd remember what to write down later. But she was too young to feel slighted by this, too in love with her brilliant father and his fantastical drawings of smoke in the air.
Then her mother died.
Her father had grown distant and cold. He would lock himself in his study or in the hermetically sealed room or go for walks in the countryside for hours. They would stare at each other silently over dinner, her father clearly having no idea how to hold a conversation with a child. As an adult, Riza met people who had no memory of their childhoods, for whom the emotions and concerns of those ages were completely alien. In hindsight, Berthold had been one of them. He could never remember the names of her schoolfriends, couldn't understand the petty dramas and fears that animated her days and held so much importance as she grew up. Eventually he shifted to taking all his meals in his study and Riza ate alone.
Roy Mustang was the one who told her that her father hadn't always been obsessed with gaseous alchemy. Before he had met her mother, before they had retreated from the world, when he was still in university, Berthold was known for his work in phlogiston theory and elemental fire, a particularly quixotic but tantalizing field of alchemy.
During the late nights at the table as they did their homework, Roy also told her about her father's attempts to model the atmosphere, how he followed Berthold on long hikes across the countryside carrying a heavy pack filled with anemometers, barometers, thermometers, hygrometers, and other scientific equipment that he'd have to set up, monitor, and record their measurements in heavy notebooks that Berthold would pore over when they returned to the study. Roy complained most about the occasions when Berthold wanted to study storms and Roy returned wet and miserable, looking like a drowned rat.
But it wasn't until her father had given her the tattoo that she learned what he had been doing in those lonely years and had been able to put the pieces together. Desperate to rekindle the happy days when he had performed for her, she had agreed to the tattoo. And indeed, he had revived his habit of talking out loud as he worked. That was how she learned he had refined his gaseous alchemy to create and control ribbons of alchemized oxygen from raw air, no longer needing carefully filled pressure vessels of specific gas mixtures. That the colored smoke was a no-longer-necessary aid to help him master controlling the motion of the oxygen, keeping the ribbons intact instead of re-mixing into the air. That he had created models of atmospheric physics and chemistry that let him extend gaseous alchemy into uncontrolled environments. That the properties of the alchemized oxygen were carefully calibrated so it could be ignited.
She had been a teenager then, ignorant of the larger alchemical community with its fads, rivalries, secrecies, jealousies, and one-upmanship, and had no idea the leap in knowledge these theories represented. Not just one lifetime achievement, but three: unsurpassed control of gaseous form, a modeling system that could extend gaseous alchemy into uncontrolled environments, and a complete theory of combustion that pulled together current immature hypotheses and research regarding oxygen and decisively overthrew the waning phlogiston theories.
Three lifetime achievements that came at the cost of his wife, his daughter's childhood, and his sanity and health.
Three lives ruined. Three lifetime achievements. Equivalent exchange.
Roy Mustang, when he had decoded the tattoo, had been the one to offer the context of exactly how big a deal these discoveries were. He had known something about Berthold's research from his apprenticeship and during his time in the Academy had come to realize how novel it was, which is why he had been anxious that Berthold should join the State Alchemist program to fund the completion of the research. What they discovered in the tattoo had surpassed even Roy's high expectations.
It had been in that decoding and in the work of turning theoretical knowledge into practical that Riza had picked up some alchemy. She didn't have the chemistry expertise that Roy had to create the transmutation equations in her head or to apply the alchemical energy correctly to trigger the transmutation of the material or control the form. However, she did pick up the knack of alchemical spectroscopy, using alchemical energy to identify the emission spectrum of atoms and accordingly identify them, to measure and observe them, usually done immediately upon activating a transmutation circle to allow intent to compensate for any unexpected irregularities.
That was how she became the best damn sniper in the Amestrian military. She didn't need a spotter to estimate the wind based on the ruffle of the leaves or the curls of dust over the sand dunes or estimate the density of the air based on their altitude or the heat shimmers above the ground; she could precisely measure and observe the flow and the density of the air over the whole trajectory. "Garbage in, garbage out" was the saying: your compensation was only as good as the data you fed into your calculations. She used standard sniper compensations for gravity, spindrift, and the rotation of the earth, but her inputs for the air were the best, therefore, so long as the biomechanics of her shooting were sound, her shots were the best.
Of course, she always had a spotter anyways. Riza never told anyone at the Academy about what she could do. She had sworn to keep her father's alchemy safe, protected, concealed. She could never really figure out how to talk about her father anyways, even in a more general sense. Sometimes she missed him desperately, missed the happy days of her early childhood, regretted that she had never figured out how to repair the broken bond between them. Roy had told her Berthold's last words and sometimes something in her ached to know that he had cared, that he had loved her, but hadn't known how to show it. Other times she hated him for his neglect, for his lack of even trying. She had been a child; he had been the adult. Why should it have been her responsibility to repair their relationship? What kind of warped inversion was it for a child to have to console a parent after the death of the other?
Rebecca had figured out that her family was a sensitive subject and kindly never poked at the scabbed wound on her soul, no one else was a close enough friend to approach the topic, and so her secrets remained unknown.
Then she had been shipped out to Ishval and had been reunited with Roy. He had figured it out eventually, exactly why she was the best damn sniper they had before she even graduated. They stared at each other with the burden of knowledge. From her perch, she could feel his attacks, could measure the heat and turbulence of the flames, could sense the contaminating particles that swirled as everything burned.
Alchemy, be thou for the people, protect, bring happiness…
They had perverted it. They had each used it to become talented monsters in their own way.
They watch ashes drift through the air, tossed by the winds.