The species is called Kirusagi... though these are still brand new and I'm still working on them... so... I'll make it brief... these entities exist around old temples... and if you damage the temple or did something really bad... these creatures will come for you and take your soul... to never see it again... also this will also feed the Kirusagi... the more souls they feed on the more powerful they become...

The Kirusagi hold mirrors to reply the events of the terrible deeds you done over and over again... until you go mad... that is when they will steal your soul... and eat it...