In 2127, the earth experienced "the great depletion" - only thirty years after the spiritual energy was revived, it underwent a sudden change. The "spirit" absorbed by humans will accumulate a toxin called "erosion" in the body. When the erosion exceeds the threshold, the cultivator will be "eroded" - the body will disintegrate and the soul will be annihilated. The global population has dropped sharply to one billion, and the survivors live under seven "purification domes" and rely on artificial filters to survive.
