Lifeforce is a metaphysical substance and energy source, used in most fictional Studio RGB-Newt productions, that is found in all living beings (and sometimes outside living beings, in a glowing gaseous form) to explain things like where some characters get their powers from, why some beings born out of pure celestial energy like Ink (whose species is classified as "alien galaxy lifeforce") are alive, and what holds certain planets together, among other things.
Lifeforce is a unique essence that is not only found in biological entities, but also in cosmic bodies such as planets, as aforementioned, galaxies, and minerals. Functioning similarly to blood, it circulates throughout the bodies of living beings and can even leak out of their veins should they be cut, or it can be drained out in its gasesous form (phasing through skin and other internal organs) if a powerful enough being has the necessary knowledge on how to magically absorb it from other people into their own body.
Weaker forms of lifeforce energy can be casually absorbed if found in the wild, or taken from what are known as "drains" (see the relevant section below).
Concept and development
Lifeforce was first conceptualized during the production of video games in the Flye 'n' Frie franchise as a game mechanic and plot element. It needed to be something you could collect from defeating monsters that simultaneously made the player characters stronger, but also be something that the player had to micro-manage to prevent them from having too much at a time, which lead to a limit on how much one could have before they literally blew up from containing too much energy. For story reasons, it also needed to be something that bad guys would probably want to collect for themselves too, and thus do a lot of evil deeds to get more of it, advancing the plot.
Color and form
Lifeforce manifests as a glowing gas when it leaks from a body, or during its time as a celestial entity. The colour varies, indicating different strains or types of lifeforce.
For physical vitality, lifeforce is essential. A depletion of one's lifeforce results in an individual with dull, uncoloured or grey eyes and a weakened body that can barely move. On the other hand, an excess amount of lifeforce in one's body can be lethal, as too much energy cannot be handled by certain beings, leading them to explode. Moderate amounts of lifeforce, above the regular amount, can imbue one with superpowers.
Lifeforce is highly susceptible to other external energy sources, such as electricity, water, and fire (especially lava or magma). When supercharged, it can amplify the host's abilities, or lead them to become volatile, if not properly regulated.
Lifeforce is naturally occurring and is generated by the cosmos, other celestial bodies, and by planets themselves. When it is found in the wild, outside of a living creature, it can be absorbed, either extending one's lifespan or enhancing their abilities.
Culture and ethics
In-universe, it has been understood by all cultures for millennia that too much lifeforce can be lethal, and that it is an easy enough substance to find in the wild, so it is extremely rare for someone to try to steal lifeforce from other people for themselves, as this requires also knowing the secret to doing so.
For those that do try though, they are usually perceived as evil villains in society, and frowned upon. Forcefully absorbing lifeforce into one's body from another's body against the will of the secondary party also does not physically feel good, and will even hurt both parties, which is also an easy deterrent for some people to not try in the first place.
However, some people will willingly share their lifeforce with each other, and this can feel good on occasion, especially if it's an emergency where someone has lost a lot of lifeforce. This has lead to some bad characters and villains attempting to befriend the person whose lifeforce they want to steal first, in order to have lifeforce willingly shared to them.
A weak amount of lifeforce can be absorbed from its gas form immediately as it seeps from a deceased body before it disappaites into nothing, and this doesn't have any negative health side effects, and it feels neither good nor bad to take it in this state. There are also no unethical complications that arise from this, as society understands it would just simply go to waste otherwise.
In its gaseous form, lifeforce can sometimes form a mind of its own and infiltrate non-living objects and props such as stop signs, forming characters like Stop. These sentient strains of lifeforce gas quickly fizzle out and die if they do not circulate through a host body soon, so they will even possess living beings in a parasitic manner to merge with them, which inadvertently destroys the mind of the host in the process, as the lifeforce doesn't know any better.
In some species, such as mink-mink harpies, lifeforce will circulate through certain parts of the body, breaking down toxins they come across to non-lethal levels that will not cause any damage to the individual who has ingested the toxins into their veins. However, the raw blood and meat of these species might still remain poisonous to other species, if not cooked or prepared right.
Certain materials, minerals, plants, or artifacts (like jars) can serve as what are called "drains", which can absorb or neutralize lifeforce to prevent an overflow or imbalance.
Most of the lifeforce inside these drains can be harvested later, but not fully, as forcefully taking all the lifeforce from something that contains it will start a process known as "lifeforce acidification".
Lifeforce acidification occurs when weakened, neutralized, and/or non-potent lifeforce found in drains is fully extracted past a certain limit. The material, mineral, plant or artifact will immediately begin to rapidly decay into a powder that then starts to froth up and form an acid which will burn to touch and melt through things like paper, plastic or glass, but not metal, as there it will just scratch or stain the metallic surface or roll off it. If the drain artifact was originally made out of metal, it will still decay into an acid due to lifeforce acidification, and this acid will act as described before, that is, scratching or staining other metallics and/or rolling off them.
In-universe, there is currently no explanation for why this happens, but certain scientists are looking into it.