Abyss

The abyss lies outside the planes that is everything else. It's the canvas that was painted over, the nothing pushed out for there to be something, and reality's contempt for itself. The abyss contains countless, perhaps infinite, pocket-dimensions. They form around powerful entities and the most powerful even have little areas bound to others within their domain. Between these domains are, oddly organic, cliffs and metal structures that hover in a world filled with a thick, dark red fog. Diffused light seems to come from far away in every direction, never able to push away the dark shadows.

There are no known sources about how the abyss came to be. Even the oldest records within the infernal archives mention that there is no trace of civilizations that were ancient even then. Exploring the past can be dangerous in the abyss, however. The very nature of the plane chances, burying some things and uncovering others. And almost every civilisation has tried to put weapons in place to eradicate forbearers that could prevent their claim to power. Wise abyssals know to avoid straying too far outside established domains. Ambitious ones explore anyway.

Environment

Environments here often lean away from balance. They are moist and wet or parchedly dry, scorching hot or frigidly cold — middle grounds are rare. Both flora and fauna are as likely to feed on emotions as traditional food, allowing them to take on a lot of different forms and live in places no normal life could be. But there's also no true sunlight to derive energy from — only the magical substance of the plane itself. As a result, even plants are likely to kill for survival when they can and all animals have developed brutal defenses. Not everything in the abyss will try to kill you — but a portion will, and you can't trust anything.

Every domain is a self-contained existential plane of sorts. It comes with its own climate, ecosystem — even laws of nature. The Abyssal Lord of a domain has complete control of the environment, in theory. The surroundings adjust to their Lord's personality and will. But this is also a trap of sorts. If an Abyssal Lord was ever to leave their domain, it would collapse and revert to the same chaos that permeates the rest of the Abyss. Because of this need to hold on to power, the older a Lord is, the more their home, even within their domain, is isolated and protected.

Planar Tears

There are two main types of tears between the abyss and Ailion: gates and actual tears. Gates are ones created intentionally through magic. If they are formed from outside the abyss, steps can be taken to hold them open over time, while those from inside can only pull one or a pew people through. Those who know what they're doing when creating a gate will anchor two specific locations together, but some amateurs inevitably end up in some random location. And a random location in the abyss is unlikely to let you survive for long.

Unintentional tears happen because the fabric of reality has worn too thin to keep the abyss out. This is often a combination of some dramatic event and intense use of magic from the abyss. The more use of abyssal power, the less is needed to pierce the barrier. Every orbit of the Moirai heals reality some and pretends this build-up. But where it's been worn down continuously, a burst of power might be enough to create a small opening.