So, the Otherside has been mentioned a few times now, and I think it’s apparent that it’s a major part of the setting and the story. That makes this a good time to talk a little bit about what it is and how it works. I’m going to start with just describing it and listing out some common phrases and ideas that are widely known in-setting, and then discuss some more abstract details about how it works.

One thing to keep in mind, while reading this, is that my usual caveats about incomplete information apply strongly here. The Otherside is a complex topic with a central role in this setting. Even setting aside the complexity, there are a lot of things about it that are closely-kept secrets. I’m going to be discussing the mechanisms and abstraction in more depth here than a lot of people in-setting think about, but it’s still being simplified, and I’m not going to be revealing or highlighting those secretive elements.

Additionally, while I say this is an introduction, it’s still a lengthy discussion. This is a topic that has a great many facets, and even with this, there are still many things I’m not touching on. My writing process for the Otherside has a lot of thought put into things that most people are probably not very interested in, and most of this information isn’t necessary to understand the story.

 

What Is the Otherside?

So, let’s start with the most basic question: What is the Otherside? Well, to start with, that name is a little incomplete. It would be more aptly called something like the Otherside network or system, but people routinely drop the latter part when it’s clear what they mean. It’s more like an adjective than a noun, though, hence why things associated with the system incorporate it that way. Otherside portals are a notable example of this.

Within this system there are innumerable domains. Each one is basically a self-contained world, and there’s a huge range of variation between them. Some of the largest are the same approximate size as the entire mortal world, with Faerie and Limbo being the two most frequently cited in that range. But others are much smaller, the size of a city or a province. There are more in that size range than of the largest domains, by a wide margin.

The last step down is a personal domain, which is essentially the equivalent of a mansion. It’s self-contained rather than being built in another domain, which is useful for a whole lot of reasons. These are the easiest kinds of domain to make, in numerous ways. They’re still very difficult, but it’s feasible enough to make a small domain that it’s sort of like a status symbol. Ideally you want to make your own, because that offers control over things that are not otherwise possible; if you don’t have the skill, you can buy one.

There is an important caveat, on the topic of personal domains. I describe them as the lowest rung of this metaphorical ladder, but that’s a bit of a simplification. Very powerful beings also have personal domains, and those are going to be seen quite differently. Nephele is hosting this party, for example, in her personal domain, which is a large and important enough place to do so.

There is no estimate as to how many domains there are, once you start including smaller personal domains. It’s not really possible to guess. The history of this setting is quite long, and there have been a lot of people to make domains. As a Fermi estimate, I would gauge it in the tens of millions. That’s as narrow a margin as is available. The vast majority are of no interest at all to the vast majority of people.

Even the smallest domain, though, is a self-contained world. No amount of travel by normal means will take you out of it; it’s the equivalent of trying to travel past the edge of the universe in a Big Bang cosmology where that doesn’t even make sense as a concept. What happens if you try will vary widely by domain, but in no cases can you travel to a different world without the use of magic. This is one of the reasons that having your own domain is so nice; it’s almost impossible to access if you aren’t supposed to be there, by and large.

Travel between Otherside domains mostly involves one of two methods, like Saori described earlier in this book: Portals, and Ways. No one knows the full history or metaphysics involved in these types of working, or if they do they aren’t talking about it. But the experience and basic nature of the two are very different, and very easy to distinguish. Ways are essentially always the preferable option, in numerous ways. They’re safer, the experience isn’t hellish, you don’t need to perform a fairly complex working. But portals are vastly more flexible, and most personal domains do not have any type of Way attached to them, because those are so difficult to create.

Thus, while not everyone is as blasé about it as Saori, most people use portals at least occasionally. Most people also only visit a handful of domains on any kind of regular basis, in part because portals are difficult and require you to know the destination very well. Generally speaking, the largest Otherside domains are also the most trafficked, and the most important. The three most prominent are Faerie, Limbo, and Earth.

Because the mortal world is an Otherside domain, in this setting. This isn’t a secret, either; most humans and even most humans who are involved in the supernatural aren’t aware of it, but if you look into it much you can find this out. It has unusual properties, but it’s not fundamentally set apart from the Otherside system. This is also one of the reasons it’s called the mortal world rather than the real world; it is no more real than any other domain.

This is an interesting quirk of perspective, when the viewpoint character is from this world. For Kyoko the prospect of seeing the Otherside for the first time is daunting. Stories in folklore about the Otherside, or rather about worlds that I have folded into the Otherside system, are wild and surreal.

But it would not, on a cosmic level, make sense in this setting to describe it that way. Kyoko’s first trip to the Otherside is not a shocking voyage into a strange, impossible world. It has more in common with someone born and raised on a cult compound learning that the world outside its walls does not resemble what the cult told them it was.

This comparison may also hint at why characters like Saori and Capinera talk about Kyoko’s first introduction to the Otherside like they do. The phrase does not exactly make sense when Kyoko has been in the Otherside her whole life already, and those two might well know that the mortal world is itself a domain. But if I were escorting a friend out of a cult compound and showing them broader society, I would certainly prefer to do so in a controlled, careful way. Going from a remote cult compound with few enough people that you know them all by name directly to the heart of a metropolis would be overstimulating in the extreme.

 

How Do People Make Domains?

So, earlier I mentioned that making a personal domain is very difficult; this is a deeply complex kind of magic. Even an Otherside portal, the simplest common type of magic that interacts with the Otherside system, is an extended and complicated working for most people. Being able to make one in under half an hour is pretty good, and most people can only create a portal to a small number of places; as a loose estimate, I’d say that for people who are of average skill and travel routinely, having twenty destination points is doing pretty well.

And that’s the simplest option. Other magic is even more difficult. A temporary Way is out of reach for most people. A small personal domain, suitable for use as a single person’s mansion, is about as difficult as a temporary Way. A moderately large domain, about the size of a city, is on par with a permanent Way. Producing and maintaining a very large domain, such as Faerie, is going to require one or more of the great powers in this setting. It’s the purview of people like gods, or the rulers of major factions. The process of producing a vast Otherside domain like that is probably the single most complex, difficult working that can be performed in this setting.

You might think of it by comparison to working with computers. This is a comparison I use often, and it might help to provide a sense of scale. Creating a personal domain is, in this sense, the equivalent of producing a high-quality website, a decent indie video game, or a program for a particular, niche application. This isn’t trivial. I’m guessing most of the people reading this have not created a high quality video game solo. But it’s not impossible to learn how, even for someone with access to only normal, civilian market tech.

Producing one of those mid-size domains, in the same framework, is more like making a major video game release, a large-scale commercial program, or major corporate intranet. This is a much bigger project. Major game releases can involve hundreds of workers and take several years. Doing it solo represents a massive body of work, far outside of the reach of most programmers and developers.

But making one of the biggest domains is, in this comparison, more like making a major operating system. The Linux kernel has over thirty million lines of code. It represents the work of thousands of contributors over the course of more than thirty years of development. That’s not out of reach in the same way that even an intricate game is. It’s a colossal endeavor. Not by coincidence, it’s also one of the most important pieces of code in existence. Over half of developers surveyed have written software for Linux, most websites run on it, and all of the world’s most powerful supercomputers run on it; Android is a derivative system, which means that a large portion of mobile devices are ultimately relying on Linux. This makes it a good comparison for some of the largest and most important Otherside domains.

You might be wondering why it’s so hard. Simply put, it’s because there’s very little tolerance for error and it requires working with particularly abstract, fundamental ideas. You need to interact with the Otherside system itself, with spatial dimensions, and with other foundational rules of how reality works. And if you screw up, the domain will be unstable and dissolve, potentially with people still inside it. Such people have never been recovered, and nobody knows entirely what happens to them, but nobody wants to find out firsthand, either.

So if it’s that complex and difficult, and has that kind of existential risk involved, why do people do it? After all, they could just use the domains other people make, right?

Well, yes. And most people do. But there are some enormous advantages to having your own domain, for the right kind of person. Privacy is guaranteed; if the only route in is by portal, and it’s not possible to make a portal somewhere you haven’t been, anyone who gets in must have been there before. If you restrict access to people you trust, and maybe their escorted guests, this stays a very small pool of people. There are very, very few ways around this kind of limitation.

Meanwhile, if you just want a very specific, very personalized kind of space, you can get that even if you don’t build the domain yourself. Someone will do it for you by commission, and you can give them whatever specifications you want.

But you do not get arguably the biggest advantage, which is the power of being able to reshape reality itself. This is sort of the tradeoff to the complexity of the magic. You need to define and adjust ground rules of reality, but that means you can define and adjust ground rules of reality. This applies even after the domain is made, and only for the creator or creators whose magic was used for it. For complex reasons, this actually cannot be transferred like ownership can; it’s not the same as, for example, having a password restricting access to those functions.

Many of the most difficult, obscure workings require this. If you want to screw around with the rules of spatial dimension and geometry, it will be almost impossible anywhere that you don’t have this access. The same goes for intentionally modifying the rate of time passing, truly massive restructuring of physical objects, changing things like whether gunpowder is combustible…the list is endless.

This is part of why personal domains are particularly common among advanced practitioners of magic. In part, it’s that such people have the most ability to create them. But another part is that they enable work that the most advanced practitioners of magic care more about than anyone else.

Another interesting note is that it allows for things like Nephele’s castle to exist. This is part of why it’s so much more shocking for Kyoko than Saori. If you want to make a gargantuan castle out of clouds, it’s easier to change the natural laws of a domain to allow for that to be a thing than to change the behavior of clouds that far from their natural state on earth. It’s easier to produce vast construction, and you can change details of gravity or material forces to suit. Having a castle the size of a small city is ludicrously impossible in Kyoko’s world but mostly represents an aesthetic choice for Nephele, not a grand construction project.

 

How Does It Work?

Okay. So, the first two parts of this essay covered in broad strokes what the Otherside system is, how people see it, and how people engage with various facets of the system. In the final section, I’m going to focus on how the underlying structure works and why. Most of the information in the first part is essentially common knowledge that most people can be assumed to have at least a basic understanding of. The same can’t be said for the next section.

But this material isn’t really secret either. It isn’t common knowledge for a simpler reason: The kind of person who defines “common knowledge” has zero interest in it. You might think of it as being like obscure mathematical topics; sure, you can look them up on Wikipedia without issue, but how many people will ever care enough to even learn the notation for Zermelo-Fraenkel set theory?

Thus, this part of the essay is more oriented at discussing my process for creating this part of the setting than something I include because it’s necessary in order to understand the story. It is unlikely that most of this material will be relevant to the narrative, and there’s a good chance that like most people in the setting, most people reading this will have little interest in the technical details. If so, you can safely ignore them; they are not required to understand the narrative.

Each domain in the Otherside occupies its own space. You might think of this as an extension of something I mentioned some time ago, in the Magical Mechanics essay. There, I commented that position is one of the few ironclad rules in this setting. In that context, I mentioned that making there be more (or fewer, for that matter) than three spatial dimensions is extremely difficult, but possible. Otherside domains don’t exist in three spatial dimensions, but they’re still subject to the strict rule that things occupy defined locations in space.

This is important, in part because it suggests some things about how magic involving the Otherside network functions. Creating a domain is extremely difficult, in part because it does involve some manipulations of spatial frameworks, and that’s a particularly challenging thing to do with magic. But even for people who aren’t strong enough, aren’t skilled enough, or simply don’t care to go to the effort of making a domain, this kind of magic is often still relevant.

There are two main ways that people move between domains, portals and Ways; other methods exist but are niche in user base and application. And it would be easy, looking at these two kinds of travel, to think they’re very similar. Since they’re used for the same thing, even people in-setting often assume they’re basically the same kind of magic, that a Way is just a stable and lasting portal. This is incorrect. You could, in principle make a portal that lasts indefinitely, but doing so would be considerably harder than making even a permanent Way, and it would still be as miserable to use as other portals. Thus, it’s only even a relevant idea for people who are doing particularly advanced and abstract research.

Portals are, however, easier to make than Ways by far. This might seem incongruous, but it’s not. Portals are easier specifically because they do not need to be stable for a long duration. Ways actually do; even temporary ones need to be much more stable connections than a portal. Making a transient portal is easy, but that type of connection is extremely difficult to actually stabilize. They’re not the same kind of magic at all.

This is not the only way in which people often don’t really know what they’re doing with the Otherside. It is, for example, generally understood that in order to establish a portal you need to know your destination very well. But why, and why does it not matter whether you know where you’re departing from? Well, in order to establish the connection, you need to be able to tell the spell which points you want to connect. You need to be able to provide that information with a high degree of specificity.

It’s easy to do that for your departure point. You’re standing right there. You can put that information in simply by referencing your surroundings. But you cannot simply say “I want to go to my friend’s house.” You need a much more specific and concrete definition of the destination than that. If you make a mistake, there are a number of ways that things can go, and none of them are good. Most likely case, whatever definition you’re putting in doesn’t actually describe anywhere at all. The portal will never form, if that’s the case.

That’s also the best case. The other major way it can go is that the portal forms, but you don’t have an actual connection to the other location. Nobody knows what really happens, at that point. What is known is that when someone steps into such a faulty portal, no one ever sees or hears from them again. The most common suspicion is that such people are in some sense trapped in transit, possibly forever. Given that the experience of a portal is hellish even when it only lasts a moment, this is a deeply horrific concept for people in this setting. As a result, most people are extremely cautious about what destinations they try to use for a portal, sticking to ones that they’ve specifically and actively studied.

There are rumors of people learning to make such portals intentionally, so that they can subject their enemies to this fate. But nothing concrete, and this type of failure is rare enough to make it unlikely. By the time someone’s good enough to do that, they can also do plenty of other horrifying things that are much simpler and more reliable, so it’s kind of a pointless skill.

How do you define the location you’re aiming at, though? This is a more complicated question than it might seem, because location is relative and the Otherside network is dynamic in structure. All Otherside domains are in constant motion relative to each other in an n-dimensional aetheric space. How do you tell the spell exactly where to look?

That’s where it gets complicated, and it’s why I say this part of the discussion isn’t something most people care about. They do it intuitively. They study the place, learn what it feels like to them personally, practice at creating that feeling in their mind. That’s good enough for most people’s needs.

But in reality, the spell is doing something pretty specific that they aren’t aware of. Each domain has a specific set of reference vectors. This is essentially domains that it maintains the same relation to, even while all of the system is in flux (establishing these is also very difficult, and a large part of what makes building a domain so hard).

And so, you don’t need to say exactly where a destination is. You just need to put in a list of reference vectors, specific distances and dimensions of travel in which something lies. There is only one domain which consistently maintains that exact set of vectors. Normally domains only need about three of them. Many smaller domains only have one, even; they’re tightly bound to a single, large domain.

This has several advantages. It means that you can travel between those domains easily. Every domain that’s associated with Faerie can reach every other domain associated with Faerie simply, because they will all be proximate to each other. They have to be, since they’re all proximate to Faerie at all times. Only needing one reference vector simplifies the process of creating the domain.

It does have drawbacks, though. For one thing, you’re now dependent on that domain. This is part of why people prefer to use large, stable domains for this. If your reference vectors all point to domains that then cease to exist, you will not be able to find your home again. If a Sidhe Queen becomes really pissed at you, it is possible for her to simply sever such a connection, too; she has fundamental enough access to Faerie’s structures to do that. Without redundancy, this, too, creates a severe problem.

The intuitive model people form, then, is going to contain this information implicitly. They don’t think about the vector dynamics. But when people talk about learning a place so well that they cannot mistake it for another, such that they can provide the portal spell with the target location as exactly as they define the place they’re actually standing in, this is part of what that means. The other factor is defining the place within the domain. A portal can, in principle, access any location in any domain as easily as any other location, with very few exceptions.

In practice, the fact that people do it intuitively means that it’s not that simple. People talk about this in various ways. One of the most common elements is that it’s easier to travel somewhere in line with your own nature. Capinera, who emphasizes sound a great deal in her understanding of the world, needs somewhere with good acoustics. This isn’t necessary for the magic itself, but it’s how she’s approaching the necessary vectors.

In turn, this might suggest something else. Once again, comparing this to the Magical Mechanics essay reveals something interesting. There, I mentioned that one of the main rules about magic is that the more you change something away from its nature, the more difficult it becomes. I also mentioned that this is because you need to be able to define what you’re doing exactly, rather than leaning on an existing, straightforward conceptual model.

That’s essentially what’s driving this. People do not use strict, logical definitions for this. They use, in some sense, the intersection of their own nature and the space that they occupy. This makes it much simpler to do. You can, at that point, essentially bypass the need to retain clear vector information. You learn how to identify the experience when you are, yourself, in that space and to simulate it.

Since the only way that exact experience happens is if you are present in that location, it effectively encodes the reference vector points. Since you are yourself present in the place you’re starting from, you can provide that information to the portal spell along with the experience. The spell people use to make a portal is designed to, essentially, do the following: Identify the nature of a person’s experience in the place they currently occupy. Take as an argument (in the programming sense) the known information about a person’s experience in another place. Use the shared element of the person to find what would need to be different to produce the exactly-defined state it was given. Transition in those directions, gradually moving closer to the correct destination, until it finds an exact match when it simulates the known person in the target destination and matches it to the known information about the person in the desired place.

Then, and only then, does the portal actually form, allowing travel between the two designated places it now knows how to find.

Now, obviously, most people do not know that’s how portals work. This is an incredibly intricate working, particularly because it has been streamlined enough that people with moderate skill can do it. Someone, and if anyone knows who they aren’t telling, developed the portal spell a very long time ago and disseminated it. People learn to create portals by imitating someone else who already knows the same basic spell. Neither the person showing them nor the person learning how to do it, ultimately, knows how the spell works. They have no reason to care about the intricacies of a working far, far more advanced than they could create from scratch themselves.

This also hints at a final implication: If you are advanced enough, many of the rules don’t stay the same. Because I, and characters in the story, have said that you can only make a portal to a place you know extremely well. But that’s not strictly true. You can only use the portal spell people know how to use for that, because it relies upon the intuitive experience of the destination, which requires you to have experienced it in the reference memory.

If you know how that spell works, it can be essentially reverse-engineered. You can tease out the portal mechanism itself, and split it out from the process of calculating reference vectors. You can then put the vectors in yourself, directly, and produce a portal. This takes much more skill and a set of vector information most people have no knowledge of, even in domains they use for portals often. It’s also far more likely to create a portal despite not having a connection in place, at which point you vanish to a presumably-awful fate.

But if it works, it can take you literally anywhere. The destination doesn’t have to be familiar, just known. The target can be any place within any domain, whether it has anything to do with who you are or not. The normal rules of travel break down, and someone can do things that most people in the setting would swear are completely impossible. The implications of all of this are left as an exercise for the reader.