THE DESCENT

A Tethys Consolidated Extraction contract

Logline

An ocean planet has one wound in its seafloor, and it goes all the way down. A corporation ships you there, sells you a submarine on credit, and gives you a licence to dig. The deeper you go, the more the rock looks like it was built.

Hadra

Hadra orbits a dim red dwarf 31 light-years from Earth. It is slightly smaller than Earth, with a radius of about 5,200 km, and it has no land at all. A single ocean covers the whole planet under a permanent overcast. The only feature anyone has charted is the Throat, a vertical fissure 400 m wide in the seafloor.

The first survey probe went into the Throat in 2193 and sent back two readings that nobody has explained since.

The rock was wet. Two kilometres down, the probe broke into an open cavity full of liquid water, and there was another one below it. Hadra's crust is honeycombed with voids, some the size of a room and some the size of a city.
The echo. The probe fired one deep sonar pulse straight down, and the return came back 28 minutes later. That is the time sound needs to travel about 5,000 km of rock and back, which is nearly to the planet's centre. The shape of the return reads as open space above a solid surface, and the return was louder than the pulse that went down.

Hadra's centre should be dense, hot and solid, but the echo says otherwise. The official survey lists the Throat's depth as 5,000 km (estimated). Nobody has been there.

Tethys Consolidated

Tethys held the only licence to Hadra from the Colonial Registry. It does not employ divers. It ships them in.

You sign a Descent Contract on Earth and spend nineteen years in cryo aboard a Tethys hauler. You wake up already in debt for the passage, the hull, and the air.
There is no ticket home. A return berth is sold like any other upgrade, and it is the most expensive item in the catalogue.
Tethys buys everything you bring up and deducts it from what you owe.
Everything in the catalogue is modular: hulls, drill heads, manipulator arms and sonar packages. Sonar is priced highest. The catalogue copy reads "Knowing is cheaper than guessing."
Your first hull is the BT-01 Tender, an 11.5 m bathyscaphe that is reliable and cramped. Most contractors die in one. Tethys considers this acceptable, because the BT-01 is cheap to replace.
Larger hulls (the Pilgrim, the Warden and the Cathedral) come with wider drills. The catalogue does not mention that they won't fit down your old tunnels.

The only company presence on the surface is Anchorage, a floating platform above the Throat. The Earth hauler comes back every nineteen years. Nobody on Anchorage has ever seen what it carries away.

Wet Rock

Tethys geologists call the voids wet rock. The water inside them is warm, fresh and slightly conductive, and three things about it are wrong.

The pressure is too low. At 20 km down, the water should crush any hull ever built. In most voids the pressure is a fraction of what it should be, as if something is holding them open.
Some voids don't follow that rule. These "honest" voids carry the full pressure their depth predicts, and a hull that breaks into one implodes. Crush-depth ratings exist because of them, and sonar is the only way to tell an honest void from a safe one before you drill.
The voids connect. They form routes that lead downward. Contractors joke that the Throat wants to be descended, and the joke gets less funny the deeper they go.
The Strata
Depth	Name	What's there
0–2 km	The Throat	Black basalt and silt. Wrecks of the survey probes. The last dim red light.
2–10 km	The Honeycomb	Porous rock and the first voids. Common metals. Most contractors never leave this band.
10–15 km	The Seam	The rock changes character, and the instruments stop agreeing with each other.
15–35 km	The Galleries	Kilometre-scale caverns where headlights don't reach the far walls. Something here glows.
35–55 km	The Ossuary	Rock laminated in layers as regular as shell or bone. Exotic, valuable ore. Drill heads dull fast.
55–66 km	The Quiet	Sonar returns degrade. Tier-5 packages report movement that no one can confirm.
66.666 km	The Floor	Stratum Zero. Nothing cuts it. It is warm to the touch, and every eleven minutes it pulses.

The rock gets harder with every band. Tethys sells drill heads for every band except the Floor, and has never listed one for it.

Depth Stations

Surfacing to Anchorage takes too long. Tethys issues claim beacons instead: you anchor one in a stable void, and it grows into a station for docking, repair, fuel and trade, plus a fast-travel relay. The work settles into a rhythm of pushing down, digging in, and pushing down again.

Stations are the only light in the Throat you didn't bring with you. Some have gone quiet, and their beacons still transmit.

The Echo (dev-only truth)

Hadra is not a planet with something living in it. Hadra is the living thing.

The voids are its chambers and vessels, and the low pressure in them is it holding them open.
The Ossuary is its tissue, grown in layers.
The Floor is its skin, and the pulse is its heartbeat.
The ocean on the surface formed later, around it.

In 2193 the echo came back louder because the pulse was answered.

Tethys knew before the first hauler left Earth. The ore that contractors bring up is not mineral. The nineteen-year shipments go to a buyer who is never named. Contractors are sent because drones stopped coming back from below 40 km. Tethys never asked why the drones failed. It only noted that people come back more often.

Tier-5 sonar detects movement because things move down there. Most of them are small. Most of them.

How It Reaches the Player
Black boxes from dead survey probes.
Tethys memos with lines redacted.
Anchorage radio chatter.
Letters from Earth that are nineteen years out of date on arrival.
Sonar logs from dead contractors that stop mid-sentence.
A depth gauge that reads down to 5,000 km, though no one has ever passed 66.

Moving the story off Earth also removes the physics problem: on an alien world, water voids and a hollow core only have to be mysterious, not impossible.

Another planet far. There is a signal coming from the center of this planet. Researchers are sent a one man exploration team combined with Robots (AI) and a half human half robot cyborg(player) which historically this guy a convict a prisoner sent there to examine whats the resources of the signal. 
so when player dies players should go back to last save