Let’s take a look at the iconic energy sources of the shadowed city of Duskwall, host to the Blades in the Dark game. These three substances seem related, but not interchangeable. What is their relationship? There is no official stance on this question, so here is a possible answer.
What are they?
Leviathan blood is a thick, black, iridescent oil harvested from the demon whales of the deep. Leviathans are incapable of dying, and when their blood is harvested, it lives on. The blood is taken by massive ships that lure the leviathan in close, puncture it with tube cables, and drain as much as possible before the giant demon escapes.
Lightning oil is a plastic liquid that glows bright blue in the presence of life, and is otherwise milky and opaque. The oil acts as a battery, draining to charge energy-driven devices, and able to recharge somewhat when underused. It does not exist in nature, but must be refined through alchemical processes.
Electroplasm is a residue of life energy from all living things native to this dimension. It is ethereal and wispy, it feels like a cold mist, it glows. It reacts to currents and breezes in the adjacent reality, not this one. (Some call it the Veil, others call it the back of the mirror.) In times past, this residue would evaporate into the background energy of the dimension each time something dies. Now that the Gates to the Land of the Dead are ruptured, electroplasm has saturated the background. Now when something dies, its energy can pool and collect, or even concentrate, until it can again affect the living.
How do they interact?
Lightning oil can be refined out of electroplasm or leviathan blood. There are also other ways to refine it, based on demon secrets and astrological calculations. The lightning oil drives the massive train network that connects the major cities, and many different manufacturers have top secret refining techniques.
At its simplest, lightning oil is compressed life energy. This life energy is fed into machines that combine runic patterns with frequency dials, tracing out the underpinning connections between elements of reality then dumping energy into them to achieve an effect with explosive power.
This energy runs lightning fences that can repel ghosts. This energy runs the massive trains that move between the cities. This energy is the foundation for the industrialization of the world.
The quality is often uneven, burning at different rates or with different amounts of “static” that can be distressing to those not accustomed to working with the industrialization of ancient alchemy and necromancy. Duskwall’s leviathan blood makes remarkably bright, clear, steady lightning oil, and it is highly prized in the wider world.
Leviathan blood is still alive. It is placed in special tanks, then doused with various chemical formulations that eat away at it. As the blood defends itself, it draws in electroplasm from the background, concentrating it in an effort to restore integrity. The tanks siphon the blended lightning oil (from the attempted melding of the blood and the electroplasm) away from the blood, so it shrinks over time and eventually loses all coherence, becoming leather and slag. Processing centers are moved often because the background electroplasm gets exhausted in an area where the process is working.
Before industrialization, shamen and other lunatics had various rituals and methods that combined human sacrifice with leviathan blood, refining it in a way until it was potent for warding, necromancy, and other peculiar purposes. These practices are now illegal.
Electroplasm is life energy. First it was discovered that certain distilling processes could reduce it from super-gaseous down to an almost-solid plastic called plasm. This material was considered an ideal resource for explosives and firearms. The process also accidentally created a form of lightning oil when the “brewer” skipped a couple steps.
Tortured ghosts create unrefined lightning oil; the electroplasm they pull into their forms has a fraction of a second before it joins with them where it is flexible enough to do anything, and harvested at that moment and condensed and alchemically charged, it can form lightning oil. Also, super-compressing space between the back of the mirror and the breathing world so that ghosts must condense destroys the thought pattern that gives a ghost its shape and will, but frees up all its electroplasmic material to flow into a lightning oil form if properly treated.
In summary, lightning oil is condensed and distilled life (whether from people or demons.) It fuels the machines of the empire, and also loads their guns. Lightning oil is widely used and taken for granted; there will always be more life to sacrifice for energy.