These 'monsters' aren't necessarily monsters at all. They are actually humans. They are trapped in a loop going through it again and again, until the actual monster achieves its desired goal. However, an Ethereal Hybrid is a Looper that is a monster, and human, that have embraced their being one in the same.
Overlife is similar to an Over World, it allows you to loop back to the beginning to fight the monster again. You can only comeback if your soulmate dies and decides to do a ritual with you that brings you both back to life to fight again against a particular monster.