Thirty Thousand Miles Under the Sea

What will it be like when there is only the sea left in this world? Thousands of years ago, the sea overflowed the last piece of land, leaving humans with no habitat or soil. In the battle between humans and sea beasts, sea beasts took the lead in completing evolution, and technology gradually lost its use. Han Chu was deceived by an alien intelligence and came to this world accidentally. There are earth-eating sea beasts, flying whales, and sea turtles bigger than a football field... What kind of magical place is this?