Basically, one concept I had in one of my mega-universes (actually a multiverse, but that's a technicality), in its modern setting (well one of them anyway), is the concept of "stashes": a cache of various things, originally just weapons but later expanded to include generic supplies, first aid equipment, various magical artifacts, and the like.
These magical caches would be unlocked by a person sending a minuscule burst of magic into the appropriate 'lock', as the key. Some stashes further require a 'code' to be entered, where someone will do something like "three to the left, five to the right". Some caches require a specific trigger, too--a magical signature from a particular element, or even coded to be a magical signature from a specific group of people. (This one's harder, obviously.)
A basic feature of these stashes would be that they are accessed before a battle has begun, or after a battle has ended, but not during a battle. Mind you, if you see an opponent with hostile intention approaching, then combat hasn't yet begun and rules favor the defender, namely, if the attacker attacks the defender before they finish, the defender will not face retribution for claiming the weapons midway through the fight. (For this reason, most attackers clearly announce their presence, make sure the defender is either not near a cache or has gotten it, and only then attack, because it's not worth the hassle.)
These stashes exist everywhere across the world, in many objects. The magical seal is perfect to the non-magical, in that the objects these stashes are hidden within never act in a way which is different from the numerous identical objects around them. But they exist a plenty. Sometimes having a single item within. Sometimes a whole horde of weapons within.
These can be anything--inside of a wall. Inside of a tile. Inside of a brick. Inside wood. Inside concrete. Inside of metal. Inside of a lamp post. Inside of a fence. Inside of a statue. Inside of a fountain. Basically, in nearly every public location, these stashes exist. (Incidentally if you couldn't tell, this is a concept I made up when I was actively visiting said places and imagining weapons within, reaching them with a magical touch, thus, why I got into the habit of touching various objects as a kid and still have that habit. Tapping something, for instance.)
This is a really nifty concept, so I decided today that I'd port it into the Rubyverse. Now, the thing about the Rubyverse is that it has a whole ton of different types of magic, and different people who would want these stashes. So, how would they be formed in the first place, and how would they be restocked? In the world that they originated from this was not an issue, but the Rubyverse would need a new explanation, and I LOVE the explanation I came up with:
Universal Donors, as they are called. Universal Donors are individuals who are entirely mundane, human individuals. They have the same capacity for magic as anyone else does, in that they theoretically have some but pragmatically have none. They hold no special attributes, no special immunities, they're just human...
...Except, they have the unique quirk that they are capable of using any type of magic...on a microscopic level. As in, they can give those short, small bursts to a stash in order to open it, refill it, and seal it again, and this is their job. They travel the world and constantly fill orders of stashes which need to be refilled. Many Universal Donors do so full-time, wandering from one place to another. Since everyone uses stashes, everyone recognizes active Universal Donors and will be more than happy to provide necessary services to the Universal Donors such that they are capable of continuing on.
Other Universal Donors are part-time, assigned to specific locations which are hard to get into unless you are a local, and stay there and are activated only when needed. Now, a rule of Universal Donors is that they can only fill a stash when there is no conflict ongoing. In a war, there must be a ceasefire. Or a truce. Or something, that is mutually agreed on by both sides. Another rule is a lack of bias, in that a Universal Donor--while they may hold lodging on one side of the war (and even have people fighting on one side of the war)--must refill stashes equally.
These Universal Donors are allowed to enlist the aid of someone in refilling a stash they otherwise can't get access to. Closing an area off. Performing memory wipes. Giving access to a restricted area. These are things a Universal Donor often needs help with. But otherwise, they don't really use others, except as a means to survive. Universal Donors are also not given a free pass to slouch off on life, at least, not by virtue of being a Universal Donor. A Universal Donor who is doing so basically full-time may be given the full luxuries of life, but they're earning their keep; a Universal Donor who refills a stash or two once or twice a month is going to be rewarded for it, but be only a part-time Universal Donor (with the reward as a bonus), needing something else to sustain themselves.
Universal Donors can have specialties. Some specialize in certain areas. Or certain types of hiding spots. Or certain items to hide. Or certain clients. After all...these people, while exposed to the world of magic and supernatural and technological, are still human. With human levels of learning and processing information. It's not like becoming a Universal Donor means you instantly know how to do any job, anywhere. It requires training and learning.
However, while those Universal Donors may have specialties, they are forbidden from having preferences, aside from the choice of how much they wish to be a Universal Donor. (Including travel or lack thereof.) A Universal Donor may inform a potential client they lack the training, but cannot refuse a job they have as within their given boundaries.
So some Universal Donors might have a specialty in, say, vampires, or supernatural creatures in general, or supernatural creature hunters (hunters don't often have magic, but they can usually fake it well enough to have a stash, which I suppose is plot-convenient for Red Hood Rider in that it gives me a way to have Herald have his weapons readily available with a justification), or magical girls (not a frequent client mind you, since magical girls tend to not need any physical thing, but they exist), or a multi-purpose stash (basically a stash that most magically-sensitive individuals can sense and unlock), and so on and so forth. But they would always have a requirement to be available to, say, create a technomancer stash.
Like I said. I really love the concept and I think it's a great addition to the Rubyverse, in that it allows for a great deal of flexibility. Mind you, it doesn't decrease drama. Just because these stashes are abundant doesn't mean they're in the location the heroes are in, for instance. (So no magical healing from a nearby otherwise-invisible cache.) Or maybe there is, but it's empty because someone else recently used it and it hasn't been refilled yet. But it gives a lot of ability for me to have a choice in things.
Another thing I thought of, and this isn't really specific to the Rubyverse per se, though it does apply to it, is that I was trying to figure out why gems are so universally considered magical, in that they often are seen as magical amplifiers and are seen as magical storage in that they store magic, and often focus it, and amplify it, and all of these various things for gems, no matter the type.
Magical gems (as in, gems that don't really exist). Crystal gems. Magical crystal gems. Diamonds. Rubies. Emeralds. Sapphires. There are literally hundreds I could name (a bunch from Steven Universe, a bunch not in the show yet but wouldn't surprise me to see eventually in there, a bunch which aren't technically gemstones yet are often considered such anyway, you get the idea), but most if not all of them are given magical properties, beyond their aesthetical, monetary, and/or pragmatic values. (Things like being the sharpest weapon available, most durable weapon available, hardest weapon available, the like.)
All of them, we tend to have that association, and I was wondering why that is. I mean. I tend to hold it true, myself. As in, it applies in the Rubyverse. Gems are good for many types of magic there. I just don't actually know why they are, they just...ARE.
It's something which I'm honestly considering trying to google, to see if maybe the internet holds an answer. You'd think that'd be ridiculous, but I'm not actually sure it would be, thanks to just how common this concept is. It has to originate from somewhere.
I mean. I KNOW that I can look up the magical/symbolical meaning/power/strength/use of these things. There's entire websites devoted to the subject. You could read for hours the various properties of a Ruby and what different Rubies symbolize and mean and do and are supposed to accomplish and the like. That, I know I could do.
But I'm legitimately and genuinely curious to know if maybe there is actually a reason humanity universally ascribed this magical power to those things. Then again, maybe not. Humanity also gave magical power to basically every animal in existence in some culture across the world. Some of these meanings are self-evident, some of them are based on the history of the culture, but others, your guess is as good as mine as to how the creature became symbolic of that thing.
Who knows? I guess there's only one way to find out. Maybe if I remember I'll give an update, though far more likely I'll just forget. I thought it was an interesting exercise though. I guess I could BS an explanation, but that felt inherently wrong to me, because I felt an explanation already existed, even if not one I know now. (Yes I know the Rubyverse is my own creation, that doesn't matter because it has a life beyond me and this is one way it is beyond me.)
Right now, my best guess is that it loosely has to do with maybe them being just naturally one of the best substances at absorbing magic. Why they are so good at absorbing magic, I wouldn't know. I'd think it could maybe have to do maybe with their shining properties, that is, their interaction with light, but even there that's sketchy since there are literally hundreds of gemstones and they all have different such properties.
Oh well. It's a nice thought exercise all the same.