Leviathan

The world is submerged,

and sea monsters rule the earth.

It's been 11 years since the world submerged in water after the world was hit by an asteroid. Since then the sea creatures started to evolve and became a monsters we called the leviathan, and ever since then the human was forced to live in fear everytime the sun sets, the remaining survivors was divided and had no choice but to become a slave of rich people who own a ship that turned into cities in the ocean that we now know as the floating cities.