Thirteen regions, the creatures that live in them, and the rules of survival. Everything you learn here exists in real life.
The bloodstream connects everything else. It carries you to the organs, and from the capillaries you step out into the tissues and further on, inside a cell.
The transport network and the centre of the world. Arteries with a fast current, slow veins with valves that work like locks, and tight capillaries that let you out into the tissues. Red blood cells here are the size of a stadium, and you can ride one by hooking on with your tether.
The valves open on every beat, and you have to pass through in rhythm. Electrical fibres work like rails. The task of the region is to repair a broken rhythm that the rest of the world depends on.
The only place with air. The physics is different here: wind on every breath in and out, specks of dust the size of boulders, pollen the size of a house. You walk on a thin film of water that lines the walls of the alveoli.
The most populated region. Trillions of bacteria with factions of their own that you can trade with. Bacteriophages hunt here, and floods arrive every time the host has a meal.
Strict honeycomb geometry with streams of bile running in between. The main forge of the game: this is where resources are refined and new enzymes are made. It turns dangerous when the host has taken medicine or had a drink.
Filters, the water slides of the tubules and a salt desert. The dungeon called the Stone is built of oxalate crystals. Lose focus for a moment and you are flushed right out.
Sealed behind a barrier until late in the game. A forest of neurons, the fastest travel in the game, and the twins' memories as story finds. At night, dreams play here.
The only window to the outside. The retina shows an upside-down picture of whatever the host is looking at. This is where you first see your own body, lying in the capsule.
Sound is visible here as a wave, and you can hear voices from outside. The balance stones change the direction of gravity whenever the host tilts their head.
This is where blood and immune cells are born. A quiet region that shows you where the body's army comes from.
The cities of the immune system. You bring a sample of an enemy here to order antibodies against it, and this is also where you earn the body's trust.
The edge of the world. The Breach event: a cut, daylight, invading bacteria and an all-out battle while a web of fibrin closes the wound.
You can only get in at nano size. Highways of microtubules, along which porter proteins haul their cargo. Mitochondria work as power stations, and the nucleus keeps the archive of DNA. A cell infected by a virus becomes a dungeon on a timer: stop the viruses being assembled before the cell bursts, or call in a killer T cell and sacrifice it.
Here a bacterium is the size of a bus, a virus comes up to your waist, and a macrophage blots out half the sky.
Your first encounter with the immune system. A macrophage eats bacteria and cannot tell you apart from them. While you are wanted, neutrophils, NK cells and killer T cells hunt you too.
It ignores you and hunts only bacteria. It can be tamed: it becomes a companion and a mount, and you can lead a whole pack of phages against a bacterium the size of a bus.
A swarm. Anywhere from dog-sized to human-sized, dangerous in numbers. Herpes hides in neurons and comes back when the host is under stress. Rabies rides a nerve towards the brain, and that is a chase against the clock.
They cover bacterial colonies with nets made of their own DNA. Until you are trusted, they hunt you as well. Earn that trust, and a cytokine flare calls them in like an air strike.
At game scale it stretches for thousands of kilometres, so you only ever see a small section of its body. Weapons will not bring it down: you need allies, and a medicine the host agrees to take.
The body's own cells, gone wrong. It is built like a late-game raid: little oxygen, an acidic environment, twisted blood vessels of its own, and guards that have been bought off.
Growing costs biomass and energy. The bigger you are, the easier the immune system spots you, and you no longer fit into capillaries. You can even block a vessel and harm the host.
You can take resources from enemies and from surplus, or from the host's own cells. The second way is faster, but the body weakens, the world turns hostile, and the ending changes.
The resources, machines and recipes here are real molecules and organelles.
| In the body | In the game |
|---|---|
| ATP | Energy and currency. Harvested in mitochondria |
| Amino acids | Material for tools |
| Lipids | Armour and shell |
| Calcium, sodium and iron ions | Rare resources for electrics |
| mRNA | Recipes. Obtained by scanning and by eating |
| Ribosome | Printer |
| Lysosome | Recycling of leftovers |
| Nucleus | Recipe library |
Every type of enemy has a weakness, and all of them come from real microbiology. The colour of a bacterium follows its Gram stain, so you can tell at a glance what to hit it with.
| Enemy | Examples | How to beat it |
|---|---|---|
| Enveloped viruses | Influenza, coronavirus | Surfactant, which is essentially soap: it dissolves the envelope |
| Non-enveloped viruses | Rhinovirus, adenovirus | Neutralising antibodies from a lymph node |
| Thick-walled bacteria (purple) | Staphylococcus, streptococcus | The enzyme lance cuts through the wall |
| Double-membrane bacteria (pink) | E. coli, salmonella | Pore-punching charges. A dying bacterium releases a toxin and triggers inflammation |
| Fungi | Candida, aspergillus | An antifungal drill |
| Parasites | Amoeba, helminth | Only with eosinophil allies and a medicine the host agrees to take |
Tools: an enzyme lance, an antibody launcher, a tether, a cytokine flare and a phage whistle. Late in the game you get a CRISPR cutter for hacking viral genomes and solving puzzles in the nucleus.