This is very interesting, which is a surprise for a Kakao bullying webtoon.
By the way, the author is playing with an aspect of Christian mythology you often see in exorcism manga and webtoons: that Satan performs fake miracles to deceive people. The ambiguity of this girl (including whether she's a girl or not) could be a test of the protagonist's faith, or a sign that she's the devil.
I'm hooked. Looking forward to more chapters.