The example in the Nioh World often relies on the power of a large amount of Spirit Stones, turning ordinary humans into Great Demons in an instant. However, Gu Mo relies on his own power and the Four Souls Jade Fragment... so naturally, the demonized form isn't impossible to undo. As long as he cannot continue to pay the enormous costs, all perpetually activated abilities must cease.
But once most instances enter a demonized state, they have either lost their mind due to some conspiracy or have become completely deranged, failing to make clear-thinking and rational choices from their own true will. Hence, this process tends to appear irreversible.
Until it's forcibly interrupted by external forces—
When the end of life is reached, unable to maintain the fusion with the Guardian Spirit, the demonization will naturally unravel.
