The Three Demons originally had little direct concept of this "Doomsday Tribulation". After all, before they were sealed, the Heavenly Court was still prosperous, and the three realms were running smoothly. Although there was some chaos, it did not pose a threat of world destruction.
No matter how fierce the three wreaked havoc, they merely brought disaster upon the Heavenly Court, with limited impact on the entire Great Thousand Worlds.
But when Emperor Shitian's Star Boat flew out of the domain of the Nine Heavens Divine Court, truly returning to the Great Thousand Worlds, and saw the chaotic and broken doomsday scene outside the porthole, they immediately understood how tragic the meaning of "wasteland" was.
