Quell Memento Spirited Away

For some reason I am completely lost on how to unlock the Spirited Away achievement on Steam. I have all pearls, time pieces, completed every level in perfect moves and every other achievement but can't seem to figure this one out. It's not clear what exactly "the spirit" is. Could someone please offer at least a hint on this? I've seen it posted on Steam in a few places that this is glitched but I find that hard to believe given the number of people who have earned it.