In the year 204x, humanity have finally achieved piece. No more wars and no more diseases and no starvation. Each country helps the other. It was a utopia. A global utopia. A global utopia that many have fought for. There is finally piece on earth.
During piece time, it was decided that every country needs to combine resources so that humanity can finally fully explore the ocean. After 2 years, scientists started to explore the ocean more than before and discovered some type of wormhole at the bottom of the ocean. They postpone their explanation until they can figure out what the wormhole is at the bottom of the ocean and where it leads to.
2 days later, they decide to explore the same area again. But this time, blue people with bodies like humans but fish for heads, came out of the portal and immediately started attacking the explorers. The one who survived, made to the surface in his escape pod to warn the others. But it was way too late! The fish men came to land and terrized every country on earth.
World's military tried attacking and defending but the fishmen were too physically strong, superman like strong! After a year of fighting, it was decided that humanity should temporarily retreat. With the help of ai builder robots, humanity quickly built dozens of castles meant to keep the fishmen out and humanity save. Humanity now lives exclusive in these specially designed castles through out the world.
After some intense research, it was found out that the fish men are vulnerable to fire and extreme heat. Each caste has guards, each one of them armed with flamethrowers and other weapons. They guard the crimson door or red door that is the entrance to each caste. They are the first line of defense but not the last line of defense.
Meanwhile, military scientists are trying to find a way to defeat the fishmen and to return life to normal. They have been trying for decades but all previous plans have failed.
The military and the government keeps in radio contact with other castle
Kenji is the 4 generation "defender of the door". He has been training to defend the door his entire life but now he must face his challenges.