FTL fuel

Exotic matter, specifically negative matter serves as the fuel which FTL travel requires. The equations call for negative mass, and this substance is that mass. Honestly kind of messy to even think about.
The general idea behind harvesting and refining FTL fuel is to tap into vaccuum fluctuations utilising the Casimir Effect.
An important disclaimer here, the physics is still very much not there, and I'm mostly pulling shit out of my ass, albeit with a very surface-level understanding.
These vaccuum fluctuations are more prevalent in certain places, allowing FTL fuel to be made with any worthwhile investment. Refining it anywhere else is kind of a fool's errand, as the costs far outweight the production benefits. It's only in areas with a substantial amount of these fluctuations that FTL fuel can be made in any real capacity.
Not to be mistaken for Antimatter, that's entirely separate, and actually proven to exist.

Properties

Material Characteristics

The most immidately noticable aspect of this exotic matter is the fact that it has negative mass. This makes its behaviour very counterintuitive, as exerting force onto it would have it move in the opposite direction. It's most commonly used in gaseous form, as that's it's natural state in room temperature. It's transparent and pretty light, at least in its negative-ness.

Geology & Geography

Negative matter is harvested and refined, in a way, at points of high vaccuum fluctuations. These points are present all over, but detecting them requires a hefty amount of machinery. Places close to habitable areas like planets are particularily valuable, and often an area of fluctuations ovelaps an entire planet. Such is the case of Endured Wrath, which is part of why it's such an important location.

History & Usage

History

It's been theorized to exist ever since the 2000s, and has been a topic of intense development through the centuries, along with this specific method of FTL travel. The confirmation of its existance came in the 2530s, but the technology only reached the point of viable harvesting in the 2600s, after which FTL drives were properly developed, now with a vital aspect available.
Nowadays, while valuable, it is a necessary substance for convenient interstellar travel. It's not needed, per se, as humans got along fine in space for 600 years before it, but it sure is convenient. It's kind of like gasoline.

Everyday use

Interstellar travel. It allows the most common method of interstellar travel, faster-than-light travel, to occur. That is quite common, from warships to travelling news-merchants, to colony vessels, or to civilian craft.

Refinement

Oh christ, help.
The process is done in an area with a large presence of vaccuum fluctuations. It can be done elsewhere, as those fluctuations exist everywhere, but it's only in those places where it's actually worth the effort. The harvesting is done by utilizing the Casimir Effect and creating a negative energy distribution. This energy is then used to power photons, which are converted into matter, at a ratio of E=mc². The reason this is done in those areas is because the mass gained is already miniscule, but in lower density areas it would be even less.
And voila, you now have an amount of exotic matter, specifically negative matter. Now you can put it into a bottle and use it to work your FTL drive.

Reusability & Recycling

Once used in a drive, the matter can't really be recovered, as it is used to boost the ship's speed, losing it's unique negative nature.

Distribution

Storage

Being roughly inert, negative matter is safe to store in a sealed box at simplest. It's still a gas, but is lighter than air. Or would be, were it not negative. Because it's negative, it works against gravity, and falls down, since it would go up were it positive.

Type

Elemental / Molecular

Common State

Gas