There is no spiritual energy left in the world. The immortals kill people burdened by grievances, raise their souls as ghosts, then kill the ghosts once they've grown strong enough and take the spiritual energy they need.
What about us? Do we kill ghosts and hunt immortals?
But I see the grievances weighing on those ghosts. I see the lives they led, and the wishes they held onto until the end.
A family of five who hanged themselves and now wander a tower; a child who can't finish the last stretch of the journey home... I see the terrible things they've done, but I also see the suffering they've endured.