"Upper Sea" 

The deep sea. Known for its darkness where no light can touch. 

Even if the merfolk race created a superb light system to transform the cities in the deep sea to be as bright as cities on the land, it was undeniable that the deep sea was too dark and gloomy. 

Official paths from one city to another or from one country to another were usually brightly lit and safe from wild monsters and beasts due to special roads, but other free paths were all dangerous. 

Many Merfolk often used the wild roads for various reasons such as not having enough money to pay to use the official roads or because they didn't have the qualification to use the official roads. 

There were also many who used the wild roads to smuggle things and became illegal immigrants from one country to another. 

In such a harsh environment like the deep sea, the countries there were not so secure and there were even many dangers in the cities.