The monster king tricked him into protecting the earth's core from the monster's attack, but now that he's done that, he doesn't think he'll be able to stop the monster from attacking him again. He's still worried that the monster will come back and kill him, but he thinks that's probably not going to happen, since the monster is so much more horrible than the little girl. The monster says that the core of the earth has been destroyed, and that he can't get it back.
The monster king tricked him into protecting the earth's core from the monster's attack, but now that he's done that, he doesn't think he'll be able to stop the monster from attacking him again. He's still worried that the monster will come back and kill him, but he thinks that's probably not going to happen, since the monster is so much more horrible than the little girl. The monster says that the core of the earth has been destroyed, and that he can't get it back.