Repelgil

Repelgil in its raw form is a toxic, semi fluid, clay-like, purple material that is harmful to biological matter. It solidifies into a spherical, solid, non-toxic material upon prolonged contact with high heat. This processed form of Repelgil however was found to have a rather unique property: in Blood Crystal proximity it begins slowly consuming itself while exerting force towards the opposite direction.

[...] they drop the Repelgil inside this hole, and it slides towards the pouch. These little gears are moved when the chauffeur adjusts the lever to turn the train. You have to check before every departure and make sure that the structure holding the crystals, the slide, and the turning gears are never damaged. [...]
— A veteran teaching a new member of the BRV guild

In an open field all you can see is that it just bounces away from the Leviathan Blood, however if there's an object in its way then it begins pushing that object with it. And if the crystal is aligned correctly with both of them being inside a container then it becomes fuel for Propulsion.

Properties

Origin & Source

Native to the Calm Islands, raw Repelgil was first found by the Yulan communities due to this particular material having been responsible for the death of plants and wildlife around it. Seen as some sort of toxic waste, the folk tried to cleanse the material until they found a way to change it by having it make contact with fire.

History & Usage

Discovery

The discoveries were made public at 1665 in the Age of Ruanon, but historians suspect that Ruanon - who privatized the material - might know more secrets about it. Which is likely as they have kept the material classified from the outside world for who knows how long.