In the Isoverse:tm:, magic is the performance of miraculous feats that defy the laws of physics. While how exactly magic works from world to world, per the Greater Soulstream post all magic is in truth simply fueled by soul energy. How soul energy manifests within a Reality can vary given their differing rules and environs, and how it's channeled through living beings to exert their will - if such a thing is possible at all - likewise differs. As such, I thought it would be fun and maybe even helpful to go over how magic works in some of my more prominent settings.
Overall, you can think of soul energy/magic as being like electricity. It's a powerful force with boundless potential, but you need special machinery and circuitry if you want it to do specific things. In some worlds, the beings there are "outdated technology" that can use soul energy, but their circuitry is inefficient and ultimately limited in the kinds of magic it can express, burning out if they try to go above their limits. Others have more advanced "circuitry" and find it much easier to redirect soul energy where they want it to go. Some species seem advanced and are capable of storing plenty of soul energy, but they require some event or higher power to hit their metaphorical on button. Others need to be "plugged in" to a magical source or higher power, especially if they are born with a finite amount of soul energy to use and require some means to "charge" themselves. Some species have specialized organs that help them use magic more effectively, like parts in a computer, while others only need a "circuit board".
That's not even getting into the concept of spells and rituals, which serve as the magic equivalent of coding. In some worlds, these things are required in order to manifest one's will with soul energy. Additional catalysts may be required to cast spells, serving as "batteries", "computer parts", or shortcuts that allow the caster to circumvent a given need.
One more note is the sometimes-corrupting nature of magic. Corruption typically refers to physical, mental, and magical changes to a being after excessive usage of magic, exposure to magical sources that their circuitry is incompatible with, or degradation/flawed modification of one's circuitry. Generally this is meant in a negative sense and most commonly associated with loss of sanity, control, and health. Magic corruption stems from its ultimate sources being anima mundi and prima materia. There are, thus, two forms of corruption:
Anima mundi corruption occurs because anima mundi is the "world soul". Anima mundi is what is, is Frenzael and thus Entirety's blood, is a physical manifestation of the collective nature of an Entirety. Entirety's collective desires are held within it, making it valuable among the spiritual, the empathetic, and those who seek knowledge of the future through analysis of the present. However, it also means that excess exposure to anima mundi corrupts one with Entirety's will, with the "local" collective will being of greatest influence. Those experiencing anima mundi corruption appear to maintain their mental faculties - at times even sharpen them - but often develop delusions of grandeur and/or self-destructive tendencies, tending to seek either apotheosis or oblivion.
Prima materia corruption occurs because prima materia is an extension of Chaos. It is the physical manifestation of the madness between Entireties, of half-thoughts and potential and nonexistence. It corrupts because it's incomprehensible to both the mind and body, overwriting them both with garbage like a gen 1 Pokemon glitch and distorting one's circuitry. Prima materia corruption is strongly associated with madness, physical transformation, and excessive, uncontrollable power. Dark and forbidden magics, unsurprisingly, call primarily upon prima materia.
ok on to the worlds ^^
Siderea
Starting with Siderea first might seem a little weird since it's newer and I usually have a sort of order I go in with these things, but for this post I think it makes the most sense to start with since it's the oldest self-contained setting in-universe and as such is closest to the "source" of things. Siderea has the fewest number of rules and catches than anywhere else in Entirety due to its nature as a sandbox for the Creators, including Creation (Frenzael) and Chaos (Asena) themselves. It is absolutely rife with primordial energies, and strong amounts of pure anima mundi and prima materia are found on the planet and in its peoples.
There are, essentially, no rules in Siderean magic. Sidereans are only limited by their wills. They can move electricity, so to speak, as though it was a natural extension of their being, because it kind of is. Their potential is unrivaled; the average Siderean with no special training has at least as much innate magical power as a skilled mage in other Realities. Sidereans are not immune to corruption, but extremely resistant to it. Rigel is a great example of this: the fact that he maintained most of his sanity and control during the peak of his corruption is utterly mind-boggling, and the fact that he was returned to a somewhat normal-ish form with few ill effects and continues to live on is unthinkable. If a human dies by getting struck by lightning, then a Siderean just gets a bit singed and moves on with their life. Now rugs, on the other hand...
Naturally, some issues can arise from this. Sidereans have long assumed there are specific mechanics behind their magic, and maintaining this illusion is important, especially now that Siderea is exposed to offworlders. An apocalypse known as the End of Magic occurred when widespread and intense research into prima materia occurred in the wake of Rigel's little apocalypse, leading to a global realization that Siderean bodies and magic do not follow any sensible form of scientific logic and magic is literally just made up. This collective loss of faith, the resounding echo of "how can this be?!" instead of "oh, cool" led to many Sidereans losing their ability to use magic and literally falling apart, like an extremely exaggerated version of switching out of muscle memory. The only survivors were those who did not learn this information, did not believe it, did not believe it was a problem, or believed in the gods enough to circumvent their lack of belief in their own existences.
For this reason the gods developed Asterismorum, a language used to construct spells, and made it basic education, causing Sidereans to increasingly believe that their magic followed rules, requiring "coding" and sometimes external resources to use for anything but the most basic spells, with anyone who used neither code nor equipment being seen as simply a magician of astonishing power. The End of Magic was also reframed as an apocalypse resulting from mass corruption, creating a peril around investigating magic too closely and redirecting the passion for knowledge and reason toward picking apart Asterismorum and magical catalysts. It certainly hasn't stopped everyone, even encouraging a daring few, but the cultural taboos around disrespecting the Creators' work by robbing it of its wonder for purposes of power prevents any real incidents from occurring.
Lilaverse
Well, first off, in regards to Them, [REDACTED]
Wow, didn't that help put everything into perspective? Anyway! On to the Test Reality. Thanks to her Request to make the perfect game, Opine can just kinda do fuckin whatever. She didn't think about it too much, but in order to grant the Tested the ability to embrace whatever balls they touched she made mini-Sidereans. Tested don't have "circuitry", exactly, they're just bags full of magic juice who need only their wills to cast magic.
...Sooort of. Problem for them is that they're bound by Opine's definitions*, so they only have access to the powers that Opine permits them to. Oress Holders can only use the powers that their Oress gives them, and non-Oress Holders can only use whatever powers Opine deigned to grant them, if any at all. The only way for them to use other powers is by using other Oresses/items when a ruleset is up that allows such a thing.
Furthermore, while Sidereans just unconsciously draw in atmospheric soul energy if they don't have enough juice on their own, the Tested only have their own juice box juices. Every "spell" sips a bit of their juice, and once they're too low on soul energy to maintain their bodies they die. They regenerate soul energy over time, and this regeneration mostly stops once their body is full again. I say mostly because being bound to an Oress adds a bonus trickle, explaining why Oress Holders will undergo personality changes and the like if they go too long without using their Oress. Similarly, this is one of the reasons why they handle food weird: if they're already "full", trying to digest food produces an excess of soul energy.
* An interesting exception to this is Dicro. Because of his nature as Frenzael's reincarnation, he cannot be wholly contained by Opine's rules, hence surviving the snapping in En2rety. If he had the education, he would be capable of using any given form of magic in a manner similar to Sidereans. Dicro, however, is under the impression he's more or less like every other Tested. He and Opine both chalk up any slight inconsistencies regarding his magical capabilities to the fact that Opine had to take a dirty tainted foreign soul in order to get an authentic Marionettiste into the Test Reality.
Asthenopia
Asthenopia's world is a cryptid normal Iso world where magic is not common among its populace. In fact, there aren't really mages at all. Magic is the domain of angels and demons, and humans lack the circuitry to perform it. The magical ability of angels and demons stems from the world's god, Aztael, bestowing magic upon its guardian race. Technically magic was just given to angels, but considering that demons are just fallen angels in this setting, yea.
Angels are capable of bestowing minor power to humans to perform small miracles, but this requires a bond to be formed between the human and Heaven through faith and prayer, priming their circuits for heavenly energies. The more devout a human the more they can handle, but these are almost always temporary blessings and an Asthenopian, as I'll call them, is no match for actual magicians from other Realities. They can handle very little soul energy at once before they explode into flesh confetti, or like fucked up little angelic drones or something cool like that idk
Angels themselves have a bit of an energy crisis going on. Aztael defused into Nezthael and Khazael, the latter of whom was banished to Hell and the former being quickly stuffed into a closet by Quenael to allow herself to reign. While Khazael can still bestow their energy to demons to some degree, Nezthael is kept sequestered away hard enough and rendered mentally helpless enough that they do not grant power without Quenael's direct orders. While angels created before Aztael's split are unaffected by this, angels of each successive generation are increasingly reliant on human prayer in order to be able to use any magic themselves.
Quenael likes this, as not only does it permit her to maintain control, it also provides justification for her increasingly converting the planet into an angel-worshiping machine with no room for dissent and ESPECIALLY no room for demons. Humans need the angels to protect and bless them, so they need to live holy and faithful lives. Angels need humans to fuel them, so they must fall into place in Quenael's finely-tuned machine or risk... well, no one without the authority ever gets to find out what happens to angels who "starve", presumably because it wouldn't benefit Quenael enough to do so.
Demons work a bit differently due to having severed themself from the holy realm and descended into Hell. The original demons - known as the Demon Lords - are like the original generation of angels in that they were bestowed with vast stores of power and the ability to regenerate it. Lesser demons are humans who have made contracts with demons and are transformed into ones themselves upon death to better service their benefactor. Contracts can rewire a human's circuitry if it's in the terms and forging them is the only way for humans to become actual mages, though using magic on main is a good way to get assassinated by Heaven.
Lesser demons are less powerful than their Demon Lord, and while they can convert people into demons in turn each generation is less powerful than the last until you hit a point in the pyramid scheme where the demons are So lesser that they lack the ability to uphold their end of any contract that requires magic. Demons can remedy this by contracting directly with a Demon Lord, consuming souls, and/or through being worshiped. This is the fate of damned souls: if they do not make a contract themselves and learn humility, they are either tormented for their sins until being successfully subjugated by a lesser demon or they have their souls outright consumed.
Honestly I could go on abt shit and some stuff needs refining but this section is getting rly long so let's move on before I ramble about demon culture n shit.
Holann
Holann - the planet RPG Hell takes place on - is an interesting case. As mentioned in the Greater Soulstream post, Holann is located in a spot that has left it overly saturated with soul energy to the extent that most of the planet is an ocean of soul juice and the core is also just basically a soul. I could go on about how that affects culture and junk, but let's just stick to magic!
Holann's species have not universally evolved to cope efficiently with its excessive soul energy, suggesting that the amount of "soul saturation" has increased over the years, be it due to its position changing to a sweeter spot in the soulstream or its local stream intensifying over the past few thousand years. Demons and fae are well-adapted to it, but humans and most animals are not.
Demons, due to living closer to the core, adapted long before it became necessary for surface-dwelling beings to do so. They have tremendous stores of energy but are liberal with magic and not efficient with it, having the equivalent of high metabolisms. This is of no problem due to being surrounded by soul juice sources, but they prefer more efficient and filling forms of soul energy, like actual souls themselves. This has led to them preying on humans, monsters (which, like on Siderea, are corrupted animals and vague entities spawned from the world soul), and especially fae.
Fae are beings born from the world soul who develop sapience and proper form, unlike monsters. While technically only capable of holding small amounts of soul energy at once, being made of soul energy and so connected to the world soul means they effortlessly absorb and channel energy. While they are not capable of feats on par with the sheer strength demons are capable of, they can use magic as frequently as they desire and rarely manage to overextend themselves enough to require sustenance. This rapid regenerative quality makes them a subject of immense exploitation by demons and humans alike, though humans typically just use them as magic catalysts and act like they're morally superior for not killing them and rather (checks notes) torturing them for untold ages until someone accidentally burns their battery out by using too big of a spell.
Humans get the short end of the stick, having more soul energy stored in them than your average human across Entirety but lacking the means to regenerate it passively. Magecraft is thus uncommon and the narrative that you don't develop magic until at least puberty is spread to keep people from burning out all of their magic on frivolous things as kids. The common person tends to hoard their magic for emergencies and then never use it like good items in RPGs, saves it for their old age to make their lives easier, or burns through most of it in their youth.
Career mages are typically hired by militaries and burn through their magic quickly if they do not prove themself capable/exploitable enough to be seem as worth devoting resources to. These resources range from raw soul to weapons and equipment containing fairies or trapped souls. The former is risky, as unfiltered soul juice can easily corrupt a human; corruption is how most career mages go, though not after their superiors make them utilize that power to go out in a blaze of glory. The latter requires a certain degree of moral decay or at least a well-ingrained fear of being next in the soul collection line. I think in ye olden days people tried to eat fairies like demons did, then realized they lacked the appropriate biological and/or magical defenses against "fairy exploding their organs and then just leaving" slightly too late.
A concept I've been dabbling with is another species which for now I'm just calling the soulkin, which Euanthe would probably be one of. These are essentially a new species of human created through generations of careful breeding and soul energy feeding, creating elfs humans with bodies far better at handling soul energy. They still are nowhere near the level of demons and fae, but the soulkin can usually ingest small amounts of Soul Juice:tm: without risk, have larger stores of soul energy, and - most critically - have a small amount of passive restoration.
idk i could also go on and on abt this setting but that's the gist let's moveroni and cheese. actually wait i completely forgot that magic is all equivalent exchange shit like healing magic is so rare bc you cast it from your life if you don't have enough magic to compensate which humans generally don't, that's behind vitrail's fire/ice gimmick, demons and fae can ignore this aspect bc they're strong enough, yea
Monster Defense Squad
Well. Whatever I'm calling the planet that the humans in the party are from, anyway.
In this setting, humans are incapable of magic on their own and instead must be blessed by the gods with the right "circuitry". However, the gods do so freely when they note someone worthy, with some being more liberal with their blessings with others. Commonly the gods will bless a single hero or other figure who did right by their name, who will subsequently go on to have kids who will inherent slightly worse circuitry, so on and so forth until either their lineage fizzles out or - more commonly - the family continues to curry the god's good favor and they periodically refresh the family's blessing. The Espirandos' blessing being renewed, for instance, is marked by the birth of a child with a Princess Soul. (Wise observers might note that might be a contributing factor to Anacrusia's dad being Like That; he is the final, weakest stage of the most recent "cycle".)
Other characters are similar in this regard. Aeoria was blessed by Menthea with great holy power, and as an angelic servant of hers Laguaro is also magically adept. Calando hails from a prominent noble Acciaccaturan family renowned for its strong magic lineage, initially blessed by Accia for their scholarly minds and then Catur for their dedication to the magical arts and eagerness to use it in war. Calando fled for Reasons and sought out the Greater Underworld for both safety and the opportunity to figure out how to learn magic independent of Catur's blessing, though it hasn't been revoked. Whether that's because Catur hasn't been paying attention, because he doesn't care, or because he likes the cut of Calando's jib is up for interpretation.
Noblezza has a Princess Soul by coincidence, but I feel like his country's patron god prolly blesses the Cabalettas with magic. Not sure if Noblezza really uses magic yet or if he avoids it for whatever reason - probably because he doesn't like owing anyone, much less almighty powers - or if maybe he got his magic revoked for betraying his country, but that's a question for future Iso to figure out. ANYWAY meanwhile Rizelia and Rubato are from nothing families, Arioso's family Probably isn't important enough, and Via isn't actually from the same surface world as the others so yea.
Anyway I feel like magic users probably need spells and/or runes but I don't think I made Calando use any in erp and I'm too lazy to figure out how to speak fuckin like Latin or whatever, so Who Knows
I think there's a conception that the gods require worship or they'll die, but even I'm not sure if it's true or not. It's not in Menthea's case at least since she's the forbidden creator deity who's a child of Perita AKA Frenzael's space hooker life so she has more than enough energy to spare, but otherwise I haven't worldbuilt the gods hard enough, unusually for me, known stanner of deities Iso. At minimum this narrative benefits the ruling kingdoms, though, as the threat of the gods not blessing them with good weather and crops and protection and shit like that means the commonfolk have reason to revere the gods, who in turn enable the monarchies who enable their worship. It's a nice little symbiotic relationship if they require worship, and if they don't require worship then the gods don't really see an issue with it because they're sluts for tidy little monarchies and their tidy little territories.
Also there's the whole "anything a god wears is an extension of their being and will grant great power to any mortals who wear them in turn but will also corrupt them in body and mind" thing
Delphys
Delphys is the setting of Princess Soul Ultimatum and is pretty straightforward. It's a thick, juicy planet where the latent magic in the atmosphere will gradually warp the "circuits" of anyone who's been let in to become capable of magic if they weren't already. Spells and the like aren't required, and magic is instead fueled by passion and desire. It is a planet that encourages selfishness and decadence by nature, so it's pretty easy for any old schmuck to make their dreams come true.
Of course, this comes with Delphys being invite-only; one can only enter it if Echidna created them, Echidna had people isekai'd there (the plot of princess rpg helo), or they fell through some kind of erp hole or something. This is by design: Echidna, being one of Perita's many spawn, is aware of the unusual amount of magic she and her planet contain, and she has little interest in wasting it trying to defend it from losers who aren't sexy monster girls here to liberate cute repressed human girls.
Estral
Estralians are capable of magic: mostly minor, domestic magic, but magic nonetheless. They didn't in the beginning, but the planet's prolonged, intimate exposure to Istra led to the populace slowly mutating into something magically-capable. The level of magical potential and efficiency varies based on genetics - Esva probably has bad genes that were a contributing factor to her poor marks in Istra School:tm: - but the average Estralian is weaker than the average Holann...ite....? To compensate, however, the Istra juices staining the whole place have provided Estralians with the ability to regenerate their soul energy at a decent pace, meaning they don't permanently burn out like Holann...ians....? do.
On top of that, at that point in time Istra was still capable of using Frenzael's lingering energy to grant a blessing to people - typically only the Head Acolyte - allowing them to use minor creation magic. In Ent1rety and En2rety Heaven College's many, many brutal experiments on them on top of the starvation they experienced between Estral and Heaven College burned up that sheer godly capacity. In Al2rety, however, Sitar maintained this ability due to not experiencing any of that + being spoiled and educated enough to maintain, if not actively enhance their own magical capacity.
Earth
damn i wish i knew how magic worked here hook me the fuck UP
aaaaaaaand that's it!!!!! yaaaaaaaaay!!!!
Everything else is either some kind of interdimensional setting where everyone comes from their own distinct worlds with their own distinct rules or is something relatively undeveloped due to being relatively untouched. Okay byeeeeee ^^