Possessed (2009)

When 13-year-old So-Jin disappears, her elder sister Hee-Jin returns to the apartment of their religious-maniac mother. Tae-Hwan, a cop, who reluctantly has to take the case seriously is confronted with more and more suicides that are difficult to explain rationally. And why does the skeptical Hee-Jin, who keeps having gruesome encounters with suicides, have to keep coughing?