Gajjaingan

Having escaped her abusive mother, twenty-year-old Ji-a lives a modest life with her little sister, Su-a. When Su-a does not return from her field trip under sinister circumstances, Ji-a vows to do anything she can to get her sister back. As she and her high school friend Wonseung delve further into the mystery, they find that there might be a larger conspiracy under the surface -- a tangled web that includes a cult, a mystery, and powerful figures that might shake South Korea to its core.

(Source: WEBTOONS)