The Underworld has two chief officers: White Impermanence and Black Impermanence. Along with Ox-Head and Horse-Face, they are essential to the Underworld's operations. None can be spared.
A hundred years ago, White Impermanence mistakenly claimed the wrong soul, causing irreparable consequences. In the end, he too entered the cycle of reincarnation.
With one of its Impermanences missing, the Underworld was caught off guard when the Gates of Hell opened, an event that happened once every thousand years. Little ghosts and big ghosts alike fled or perished, throwing the already understaffed Underworld into turmoil.
To fill White Impermanence's vacant post, King Guang of the Underworld decided to borrow someone from the mortal realm with a half-immortal constitution. They would temporarily serve as White Impermanence, and once the Underworld's ghosts had all returned to their proper places, they would be granted any wish they wanted.
Unfortunately, King Guang grabbed the wrong soul. When the Gates of Hell opened, several small worlds briefly overlapped, and the soul he grabbed at random was an ordinary one, from the twenty-first century, no less.
In short, they couldn't even catch a person, let alone a ghost.
P.S. I borrowed this setup. I haven't read the book, I just thought this setup would make things convenient.
Theme: As long as you're happy.
