1.bcs that blue stone is just one of the fragments of the godess and really not that important but in a way they can use it to lure Ragibach and also identify the spiritualist just like she did in the demon world contacting with it. And also Ragibach can use it to pretend she has spiritual powers and then destroy it. BUT if she doesnt kill the actual spritualist aka Keira it doesnt do any thing. BCS ITS JUST A FRAGMENT LEFT BY THE GODDESS. The real reincarnation of her power and the real one in danger is Keira.
2.Also ofc the controlling ppl hurts them bcs they become mindless slaves and eventually kill themselves or each other. AND IF SHE EXPOSES this power than everyone will know that she aint the spiritualist and is actually from a dark descent aka the ppl would call her a demon or a dark practitioner which would further secure Keira s position and the ppl s trust which do fuel her power of the goddess within her. Since they need to worship and remember the goddess for her power to really work and purify,protect etc.
3. Also yeah the demon basically cant do much since she has not manipulated her dad,the uncle who is her pawn is dead and she herself is forced to posses a human dead body which limits her force which is very convienient.ShE may try to kill aunty though but even that isnt that easily done since everyone is quite suspicious of her.
If anything Keira has outplayed her every move by also using the demon that seems to underestimate her which will be her downfall.
still reading this, but (had to stop) as have to say - i don't get WHY the MC not telling anyone to at least safeguard the bluestone (forgot it's name) that's the contract between this world & the goddess.
so what if she is trying to find out more about how to exposé the demon in her half-sister. she also not think to inform anyone that her half-sister has the ability to control people?!? this not important info that could hurt innocent people ┑(￣Д ￣)┍
while she's away, what she thinks the demon will just sit around doing nothing???