Every fathom takes something back.
The seas rose and the surface is gone. What is left of humanity holds on in hab-shells: salvaged homes anchored in the dark, overgrown by a sea that moves into anything warm that stays still. You pilot a salvage-sub out of one of them. Keeping your home lit means diving into someone else's.
One dive, one shell - A raid is a short run through a single shell, from its outer hull down to its Pressure-Heart. Pick a route on the branching map, fight through its chambers with the deck you brought, and decide each fathom whether the haul is worth the hull. Integrity carries between fights and the depth spends it. Crack the Heart at the bottom and the harvest floods open for you to strip.
The other half is your home - Build the shell you live in: lay out its chambers, grow its defenses, and bury your own Pressure-Heart deep. While you are away, other divers come for it. Surface to the defense report, see where they got in, and rebuild the line.
Real divers, real grudges - The shells you raid belong to other players, raided and settled asynchronously: no lobbies, no waiting. Take from a stranger this season and a stranger comes for you. The ranked ladder is the deep's map of power, and your home is a name on it.
Pick your answer to the drowning - Two factions to belong to at launch. The Hold seals the shell and outlasts everything, armor and bulkheads and the patience of people who think the water rises forever. The Bellows holds the only air plant and rules by the leash: railguns and harpoons built to break a diver before the line. Both draw on the Flotsam pool, the cast-off divers' common gear.
