Leviathan

The sea level rose to cover the continents. On a planet where dry land can no longer be found, the young Bota's family lives on a small boat and wanders the vast ocean. A harpooner who hunts in deep sea water may be the prey of a monster at any time, those who only appear at night. Will Bota and his family ever make it to safety and escape this aquatic hell?... And who in the world is Kana?!

(Source: Toomics)