Flood (LEVIATHAN)

A meteor hit one of the ice caps and plunged the world into a great flood, only the highest tips of mountains and stacked toppled buildings remain. The survivors have build floating cities on boats and trading outposts on ruined building tops. Mutated fish known as leviathans come out at night to hunt, though some smaller ones will hunt during the day, and they come in a wide range of shapes and colors with unique abilities for each species. Along with the emergence of the leviathans from the meteor, a disease that causes scales to form on the skin of individuals that were affected by the meteor is referred to as the fish disease, though it isn't contagious there is no known cure. Heavily inspired by the Webtoon series LEVIATHAN, let me know in comments if you want me to actually structure it to be accurate to the series.