Long ago, a poor family was defeated by a giant hydra. The family lost all of its possessions, but the monster survived thanks to its tenth head. Each of the family's children would inherit the power of the monster. As time passed, the humans would get married, have children, and then die. The descendants of the beast would scatter throughout the world, but they would never give up. Finally, the monster created the key to the monster's shell, which he buried in a hidden place. The monster is a monster with thousands of years' experience, but a normal human cannot defeat him. The humans have suffered for so long that if they don't act, all of their descendants will suffer.