Understomachs

Their Main Food Source

Explaining rabbits when the topic is foxes.

When a person or animal dies in our world, or an alternate reality of it ("reality where Soviets won the Cold War" type stuff), it appears in the Trickster's Afterlife. They are then known as Otherworlders or Earth-Born, both of which are usually only used for humans but can be applied to animals too.

The coordinates (as in how far North, South, East or West one is) of where an Otherworlder appears are the same as the ones they died at on Earth. They appear in the deepest underground place where the air is breathable and the temperature is neither boiling nor freezing.

They Themselves

Understomachs are huge underground creatures that are essentially just gargantuan stomachs, all other parts being tiny in comparison even when put together. They fill their stomachs with breathable air using a mixture of symbiotic plants and connections to the surface. 97% of the world's surface has an Understomach directly below it.

So that's 97% of Otherworlders being Understomach food.

Symbiotes

Understomachs have entire ecosystems inside of them, plural because of how big they are as one end of an Understomach is unlikely to be home to any of the same species as the other. A lot of these species are parasitic, simply using the Understomach as a home to live in while nomming on half-melted meat in the acid oceans, the flesh of the Understomach directly and of course one another, but more interesting are the symbiotes.

These kill Otherworlders, invasive species and parasites. They remove and help prevent infections, mutations and cancers. They carry out literal surgeries on parts of the Understomach, and help it heal from bits of damage it's taken. Some of these are very intelligent and cooperative among themselves, actively acting as preservers of nature within the Understomach, and of course there are also ones that are fucking huge or can cut you in half with a flick of a claw. Some of them even take a proactive approach to protecting their Understomach, going forth from it to slaughter any potential threats they find near it.

Some Understomachs have post-human species living in them.

Internal Biomes

• Acid oceans. These are where Otherworlders appear, and so where almost if not all material and energy within an Understomach comes from. Home to acid-resistant life forms that feed on Otherworlders - both alive and dead - as well as one another. Connected to the surface by cave systems, letting oxygen flow in, but also creating potential escape routes for any Otherworlders who are resourceful, tough and most importantly lucky enough.
• Ceiling and wall lungs. These push air in and out of the Understomach's stomach so that Otherworlders can keep appearing there, as well as collecting the oxygen the Understomach personally needs to survive.
• Ceiling forests. MORE OXYGEN FOR THE MASSIVE SINK OF OXYGEN THAT IS LITERALLY A GIANT ANIMAL FILLED WITH ANIMALS. If the Acid ocean doesn't have enough oxygen in the air just above it for Otherworlders to appear there, then they often appear in these ceiling forests. These forests feed off the Understomach's blood and have their own ecosystems, such as creatures that eat the foliage so that it doesn't overgrow and suck up too much of the Understomach's blood. These are often home to intense bioluminescents, a source of light for the creatures in the acid oceans below.
• The intestines. Fleshy portals are used to transport acid full of melted flesh into caverns across the Understomach, where the acid is neutralized and then the nutrients added to blood to be transported around the body by countless hearts. Oh yeah fleshy portals are a thing don't worry about it. Creatures sometimes get into these caverns, and so ecosystems have formed in them.
• Blood rivers. Sure enough, home to animals swimming around in it. It takes absolutely horrendous luck for an Otherworlder to end up here. If anything this is the hardest place to get out of from within an Understomach, despite also likely being the safest.

Basic Information

Anatomy

An Understomach isn't just its stomach... though it is mostly its stomach and all else about one is seemingly just there to enable it.

Fleshy portals are often used by Understomachs. Blood and the pumping of hearts simply isn't enough for something as massive as an Understomach, so they also have fleshy portals. These allow resources to be moved far fasty and more efficiently, despite fleshy portals often costing a lot of energy and releasing a lot of heat. These are also used in their nervous

Cave system connection: Understomachs need to be connected to open air or the ocean by cave systems to survive, as they need somewhere to absorb oxygen while disposing of excess carbon dioxide and heat. Even if an Understomach's internal plants are enough on the oxygen front, it still needs to get rid of that heat. Each cave system an Understomach is connected to is another way for it to breathe. The fewer cave systems there are in contact with an Understomach, the less places it has to expel heat, and so more heat is expelled through what ones are available, which can create whole biomes on the surface and within those cave systems, often with endothermic plants and fungi (using heat instead of sunlight for photosynthesis) as the basis that enables all else.

Genetics and Reproduction

How Understomachs reproduce is unknown. Understomachs are often really fucking old, like the one that was underneath the sea South of Lamara was at least 70,000 years old before being killed due to a fight between two sea leviathans in which they kept slamming each other into the sea floor. That info about is was only possible to obtain because its symbiotes, which normally kill anything that dares approach their home, and it being possible to send people to do the piss rock ritual or whatever sorcery it is that lets geologists and archeologists know how old things are.

Which in short means that if they be fucking, it ain't often. None of the Understomachs within the area the story takes place in are showing signs of reproductive activity. If any could be considered juveniles, nobody even knows what things would indicate that. It's not known if they reproduce sexually at all.

More is known about their DNA, since that could be retrieved from the aforementioned dead Understomach. They have cool symbiotic viruses that help maintain their DNA, which is important since their sheer size means there are endless, potentially harmful mutations happening across their bodies. That said these viruses aren't always 100% effective, so Understomachs also have systems for destroying whole chunks of themselves and then growing back into said destroyed parts... said system is usually telling symbiotes to rip up and eat a place.

Ecology and Habitats

Living Underground, everywhere. They very much make their own biomes, or are their own biomes, or collections of biomes, pressing outwards against the rock around them at the same time as growing out into any caverns and cave systems they make contact with.

Dietary Needs and Habits

People and animals are constantly appearing inside their massive stomachs, providing an unending source of energy and biomaterial. They also sometimes chemically break down and absorb material from rock as they expand, but this is less a nutrition thing and more a making space to expand thing, and Understomachs don't expand very quickly/often... there are no known cases of Understomachs being in contact with each other, though you do get ones that overlap because some of one is far beneath another, so it's assumed that them making contact with each other results in one or both of them dying.

Behaviour

Sitting around as food literally appears ready-made in your stomach doesn't require the vastest of intellects, especially when that's paired with being home to symbiotic species that have a vested interest in keeping you alive and so have evolved to make up for your every shortcoming.

Additional Information

Uses, Products & Exploitation

Some Understomachs have human societies or organizations in them. These groups, or at least their bases within the Understomachs, are generally under constant assault from the Understomachs symbiotes, but it's not like replenishing your numbers is all that difficult when you're in a place where people are just appearing out of thin air.

The Lamaran Understomach's roof-forest used to be home to one of the bases of the Hades Society, a covert group of Otherworlders within Lamara. They wanted to get one of the Lamaran Royal Navy's steel-ships and use it to easily rescue people from the acid, but their attempts to obtain it exposed the existence of their base there. Their base was overrun by symbiotes 17 years ago due to the Lamaran Temple using an agent to sabotage its defenses, and no further bases have been successfully established there since.

It's rumoured that the Temple has a base within the Lamaran Understomach, maintained using the Temple's anomalies, but whether or not this is true is unknown. Why they'd even have one is also unknown, either to snatch up Otherworlders who might have useful skills/talents (super illegal since they're meant to be killing Otherworlders, but they've been confirmed to have deliberately overlooked people they suspected of being Otherworlders for being useful, and even deliberately recruited Otherworlders under threat of death).

Branch People claim that a group among them maintained a base inside the Black Forest Understomach*, and would sell items made or obtained within it to the other Branch People groups. There's evidence of this in some of their items. The Black Forest Understomach seems like it might die, with many parts of it being infected and massive injuries not healing as quickly as they should, and in turn its symbiote protectors aren't in tip top shape either. But, again, it was eventually overrun. It's more likely that this base was outside the Understomach and they simply went on ventures into it to obtain materials.

*This is the Understomach that Sarah appears inside of at the start of the story. Yes, the bullshit she had to get through to survive and leave that Understomach (for those aware of said level of bullshit) was basically easy mode. And I'm considering making it harder, like her having to scale the Understomach's wall and traverse the roof forest, and then having to leave out one of the fleshy caves that has a river leading into a waterfall flowing from it into the acid ocean, meaning that if Sarah were to slip and fall into the river she'd be taken to an acidic death. As opposed to just finding a hole in the side with a river flowing into the Understomach. Violent symbiotes trying to kill her and her having to use a cleaning symbiote as a meatshield would remain.

Perception and Sensory Capabilities

It's... very overcomplicated. They have lots of very varied sensory organs across their bodies, and things assisting those sensory organs like eyes being paired with bioluminescents. Organs near (within miles of) these sensory organs then have automatic reactions to different kinds of stimulation, for example if you're in the stomach-acid ocean and you touch the bottom then bone spikes will automatically lunge out and impale you, without there being any thinking about it on the part of the Understomach.

Conservation Status

No conservation laws, but no need. Anything that's a threat to an Understomach is something humans don't have the power to do anything about. That said, an Understomach dying can cause a serious shitshow. Understomachs use magic, magic in this setting being kinda weird but if anything more intuitive/naturalistic than that of most settings, to prevent themselves from collapsing in on themselves.

So if an Understomach dies, it collapses in on itself, and the ground above it collapses too. Keep in mind these are continent-sized creatures. An Understomach dying reshapes the whole landscape over a massive area, can cause extinctions and is generally the death of any civilizations, possibly any humans in general, that were sitting above it.

Otherworlders quickly appear in the area, no longer being melted by stomach acids. The period of time from here until there's a new Understomach in place (assuming Understomachs can actually reproduce and the loss of an Understomach isn't just a permanent hit to their population) is usually what creates places where the lifeforms are very similar to those from Earth, because some Earth creatures were able to establish themselves and evolve into the ones that exist later on or hybridize with local wildlife.

Humans and birds are kinda exceptions because they're the most likely to survive getting out of Understomachs, humans by being clever and birds by just being lucky enough not to immediately fall in the acid and managing to fly out.