A long time ago, the world was divided into "four" classes by a divine being: Sirens, tied with the ocean, Hybrids, tied with the nature, Paragons, tied with heaven, and Humans, tied with earth.
They all lived in harmony, until arrogance took power, causing two major wars within:
The tidefall war- A war between sirens and Humans.
Sirens thought humans were useless since they were the only class who wasn't special, blessed by the divine beings, so they tried to get rid of them. It lasted two years, and was stopped by the Paragons, who made a contract between Sirens and Humans. Humans have been scared of Sirens ever since.
The unbound flesh war- A war caused by the Hybrid, with the goal of erasing the other speecies.
Hybrids thought of themselves as superior beings, closer to the gods. They refered themselves as "children of mother nature, born by a real god", and so, they started to attack. "Earth would be a better place with Hybrids alone!", they would spit out this phrase, like someone had said it to them over and over, making them believe the lie.
The other classes were forced to join, fighting and stopping the nonsense hybrids were put into. Some hybrids managed to escape, so they're now hunted forever.