The year is 2600. A devastating war has submerged half the Earth beneath the ocean. Survivors cluster in floating harbors built from salvaged wreckage or live aboard ships kept running by aging engines. The seas are now also home to something unexpected: colossal marine monsters that represent an existential threat to every community on the water. In response, a profession has emerged — Monster Hunters who pursue the giants for prize money. They go out alone. Some return victorious. Others never come back. A young Monster Hunter is about to start his first voyage into uncharted water.