Hundreds of years ago, the star gap tore open in the sky for the first time, and alien beasts flooded into the world like a tide, bringing unprecedented disaster to mankind. At that time, human technology and weapons were almost helpless in the face of alien beasts. However, as the invasion of alien beasts continues, some humans gradually awaken to a new ability-spiritual power. They sign a contract with the alien beast through their spiritual power and borrow the power of the alien beast to fight. These people are called "beast masters"...
