Alright so I think I kinda got a little too excited But uh yea here ya go (Not related to Hollow Knight in any way mostly bc I have yet to play/watch it) Millstone is basically a spirit of stress. It is one of the Eidolons, a kinda spirit that influences every species whenever they pass by a mortal. There’s also Happiness (Nessi), Guilt, Anger, etc. There are a few, such as Millstone, that are rather summoned. The person is becoming increasingly potent in the summoned Eidolon’s field of expertise, like in Millstone’s case, stress. The summoner then kinda gets trapped in their own stress, being the one to start it. They are also the ones who need to escape, breaking the mask to free themselves. The mask revives or smt after the summoner is freed. Yea. Um, if you don’t like it it’s fine cause I had no idea it would turn out this creepy. Thanks for letting me enter tho! Credit: @Vessel_Knight for original design