The implications are so interesting, like the story and lore of this world seems to build very slowly. It seems like spirits can get malicious if they're left for awhile and are unable to pass on when they have certain regrets or things that are holding them back (something we probably all knew from countless of other mangas that have these kinds of spirit stuff). And that line where they get devoured may be where the spirits go to pass on, or maybe even where spirits who become conscious of their own state of becoming a malicious spirit, and decide to destroy themselves in that manner so as not to hurt their loved ones.