Great beings chosen by the Gods themselves to be champions of the realm. These 5 individuals rose up to the challenge to take on the demons in the Great Demon War. The banded together to take out all of Unknown casting them out of the realm. They took down the Key Demon and thus saved the realm from utter disaster.
The sages continued to appear at the same site where they defeated the Key Demon and bound him with chains. They called this the resealing ceremony where they would perform a ritual and strengthen the chains that binds the creature.
However, during one final ritual, the sages disappeared. There was no trace of them left to be found.