In the year 2600, following a devastating war, half the Earth‘s surface lies under the ocean. The survivors of the catastrophe live in floating harbours built of flotsam and jetsam, or on ships powered by old engines. Gigantic marine monsters have suddenly appeared in the seas, roaming free and threatening the very existence of the survivors. In this society, some men have become Monster Hunters, big game bounty hunters who pursue the monsters of the deep for prize money. These men sail the seas alone, sometimes never to be seen again, while others return to the harbours victorious, bearing the remains of the slain giants. In this new world, a young Monster Hunter is just embarking on his voyage to yet uncharted waters.