For all the many differences and diversities experienced in the Apotheon today, the one connecting thread linking them all is the Spirit World. Known also as the Spirit Realm and the Spiritual Dimension, though it is the home and birthplace of the spiritfolk and many of the monsters that haunt the multiverse, precious little is known about this realm. What is known is that the spirit world is hostile to all living beings. Indeed the only beings that can survive more than a few hours in that place are the spiritfolk themselves, some Firstborn, soul beasts and of course Ascendants.

Another, proven fact is that the spirit world is an ethereal realm that connects all worlds within the Apotheon. It exists in parallel with the physical realms and is shaped by the collective consciousness and beliefs of sapient beings across the universes. This realm pulsates with energy, swirling with vibrant colours and otherworldly landscapes and can be assessed through a variety of means. It is by far the easiest and safest way to realm-shift, though not the fastest. And safest here is relative. Each planet affects its section of the spirit realm differently and some of these are quite perilous to traverse.

In any case, travel can be facilitated through the use of an Astral Nexus, a location and/or circumstance where the physical and spiritual realms meet and become one. At least one of these exists on each planet. Usually, it is as simple as finding one’s way to a Nexus, using it to enter the spirit world, locating another Astral Nexus and going through that, back to that area's physical plane.

This tale has been unlawfully obtained from Royal Road. If you discover it on Amazon, kindly report it.

However, an often unforeseen caveat of this method is that the location a Nexus connects to is quite fixed, unlike other means of realm-shifting.

The spirit world spawns diverse manifestations of energy and consciousness known as spirits. These spirits embody various Concepts, emotions, or natural forces, taking on forms that reflect their essence. They can range from lesser spirits which are manifestations of simple Concepts and ideas like fire and water to more powerful and complex entities known as greater spirits. These can be neutral or mischievous, a few are benevolent but a terrifying number are actively malevolent.

This is also how soul beasts and monsters are formed and these manifestations are as unique as the planet they originate from. Indeed some have speculated that it is this interaction between a planet and its spirit region that gives rise to spirits and this idea is not without merit; it is rare to find spirits, lesser or otherwise far from their resident planet’s spirit region. Soul beasts have a lot more leeway in that regard, but even they do not survive long in the space between regions.

In any case, while the Spirit Realm is the most well-known and the most common of all the realms, it is not the only one. While not every inhabited world has them, some, in addition to the Spirit World, have other realms or pocket worlds overlaid over the physical plane (most famously Ingress.) These may be temporary or permanent, are usually dangerous and are best left to the inhabitants of the worlds in which they form.

— The Explorer’s Guide to the Multiverse, 2nd Edition.