It seems the consensus is essentially: Don't explain a damn thing, magic is magical, or if you want to explain, keep it relatively short.
Personally, I think magic is complicated. Explain too much and the "Magic" portion of magic become science. Do you want a science system, or a magic system?
TL;DR
There are books that go deep into the magic systems explaining almost all things, but not everything. There's a fanbase for that.
-And there are books that don't explain anything at all, allowing readers to theorize. There's also a fanbase for that.
For publishing, I'd recommend the first.
For scribblehub, I'd recommend the second.
But For honesty, taking what you do naturally, and delving into that, is the best course of action. If you're a world builder, build a world. There will be a fanbase for that.
You can skip the rest.
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Fullmetal Alchemist explains magic as Alchemy, the science of manipulating matter through Equivalent Exchange: Knowing the subject matter, and rearranging it using the law of deconstruction, and reconstruction using a transmutation circle. Easy! Until... you ask, where does the energy used by the transmutation circle come from? Your own life force, your soul. So in order to do larger and larger feats of transmutations, you need more and more life force. Enter the Philosopher's Stone. Now, you're not using bits, and pieces, of "life force" , or tiny slivers of your soul, you need ENTIRE souls; MANY souls. (this is where 2003 Fullmetal separated from Brotherhood) Sacrifice another world, "Shambala" (Earth during WW1 London around the 1910s) from across "The Gate". Or in brotherhood, sacrifice the world with the characters as we knew it.
Not too complicated, but incredibly messy. Inspirational, until it got messy.
One Piece explains its magic comes from Devil Fruits that grow off "Adam trees" somewhere in the Grand-Line. Each fruit is special in its own way, and gives a person distinct properties, which they, themselves, must choose how to use. EX: Luffy, made of rubber, gains all attributes of rubber, making for some really cool abilities, humor, and action that wouldn't otherwise be possible. In one arc, there was a "God of Lightning" and throughout the entire arc, he's made to look like such a huge, terrible, crazy, unstoppable tyrant! -But Luffy is rubber. Rubber doesn't conduct electricity. At the time it was enjoyable to watch, but looking back, it was such a nothing arc. Future arcs would become so much more wild, or outlandish, or humorous, or dramatic, or etc. But the powers continued pressing toward newer heights. Enter Haki, where it didn't just matter about the Devil Fruits, and yes I know that Haki was introduced essentially first episode, but is NOW being formally introduced. Haki changes, a ton about what we understand about the show moving forward. Characters with gag devil fruits that in no way can ever be harmful, can still be beyond dangerous if they mastered any one of the designated Haki styles.. It's definitely interesting toward plot and story, but somewhere down the line, I think it went on just a bit too long, finally coming to a close.. in a few years? I dunno.
Not complicated, and inspirational, but so dang long.
I brought these two anime up because they're both well loved in their circles, and the circles they belong to are incredibly large with many fans, and many haters. Both explain their powers, and the power systems, but also unravel larger segments of that system to grand reveals that the system can, and have been corrupted in some way or form to prove the system is not as machine-like as the characters believe it to be.
In fullmetal, the system is corrupted by the homunculi (and therefore the government) to create the Philosopher's Stone to make them human, to give back humanity where humanity can't be given, but now have to ALSO deal with gods, and other worlds, and gates, and etc etc etc..
In One piece, its corrupted by Blackbeard having two Devil Fruit powers, and Kaido who is a master of All Haki, and somehow, Luffy had to overcome those trials; While also, might I add, dealing with the government who can give random background character K a bland, ordinary gun armed with seastone based bullets, and they could possibly suddenly defeat, essentially, god-like characters of the one piece universe.
All of this throws a wrench into what we thought we knew, and shows us how things can escalate into these gargantuan titans of storytelling. (One of course being larger than the other in current times since one is still actively being written.) But this is online. It's scribblehub. And most people that are running through here are doing just that; Running through. They want a story they can easily digest, and pick up, and continue moving through as they go through their own daily lives, not having to do homework of looking back on previous chapters of why certain magic is needed to do x thing to explain why did it do what it did?
An 11 or 12 episode anime, sure, I can probably look for specific moments to analyze and remind myself oh yea, this happened, and that's why this happened, right. next episode. Fullmetal Alchemist is 64 episodes long, I can probably try to look for references of why something happened. Maybe. But One piece?? One piece is 1100+ episodes long. And searching for why something about Haki did a certain thing out of nowhere, and trying to remember what episode they talked about it.. forget it. I'll look it up on youtube later describing wtf just happened because I blinked on certain episode containing a 2 sentence description of what that specific power can do combined with Haki if this certain condition is ever met at this distinct time of day while the full moon is out and raining and you just ate precisely two oranges over a canyon facing westward. Idk, man.. Sorry, some things just need to be less in order to be more, but at the same time, if you keep up, it's fascinating, isn't it? And that's what fantasy is all about; The fascination, the imagination.
In all fairness, magic can be anything.
Pokémon is fantasy about catching monsters; Sometimes explaining Biology. They have a whole song asking What kind of Pokémon are you? How do you do the things you do?
The Last Avatar is about the elements: Earth, Fire, Wind, Water. Then they throw a left turn and add Metal, Lightning, Ice, Combustion, Hell even Blood! And they explain almost EVERYTHING.
Deadman Wonderland also uses blood as a weapon. I don't know if people would consider this blood magic, but.. that's an anime that exists.
It just depends on what you want to do. Don't fight yourself. If explaining, and world building are your thing, Let it flow through you. I mean, within reason, of course. Don't go crazy on a single page, but a sentence, or two, here, and there, sprinkled in, and for most things, like in real life, show, don't tell. You can explain every single detail, but the important thing is to reveal it throughout the story. Let the system be a character in your story; They don't have to be the one speaking, but they do speak loudly. Give it time to develop, and grow, -And maybe later, you can throw your own wrench into the mix, add another system into the machine, and find out how to combine the two. Seems to me, that's the way to make a story go into insane levels of "Whoa". (Given, writing style is also important.)
