A cosmic radiation called "Red Rain" swept across the world, causing the Earth's biological gene chain to break and reorganize. Humans are no longer at the top of the food chain, and animals and plants are evolving crazily. The city is reduced to a primitive jungle, order collapses, and only the evolved can survive.
Human beings hunt heterogeneous creatures and extract their "bloodline gene source fluid" for fusion, thereby obtaining the opponent's abilities (such as the speed of cheetahs, the power of giant elephants, and the regeneration of plants).
