AN OMINOUS GUEST

An ominous guest summary:

A horror story set in modern times with ghosts.
College student Yeongjoon has a younger sister named Soyoung.
However, after Soyoung returns from a mountain trip, she falls ill with strange symptoms, and the occurrences around her are inexplicable by science. Even the hospital can't come up with a proper solution.
One day, an elderly relative visits Yeongjoon and introduces 'Doyeon.' The elder claims that Doyeon is someone like a shaman and has personally witnessed the healing of someone with symptoms similar to Soyoung's in the past.
Despite not believing in ghosts, Yeongjoon, desperate to save his dying sister, seeks out Doyeon with determination, only to face repeated setbacks.
Then, one day, starting with the doorbell ringing at Doyeon's house, horrifying events unfold for them that cannot be explained.