Revenant

When the door to another world opens, demons exist there. Ku San Young is possessed by one of those demons. Yeom Hae Sang can see the demon which has possessed Ku San Young. They try to figure out the truth behind the mysterious deaths related to the five sacred objects.
Ku San Young is busy working part-time during the day and studying to become a low-ranking public officer at night. One day, she receives some articles left behind by her late father. Since then, mysterious deaths take place around her. She also finds herself slowly changing.
Yeom Hae Sang comes from a rich background. He teaches Korean folklore at a university. Since he was a child, he has had the special ability to see demons in this world. He even saw his mother get killed by a demon in front of him when he was young. Yeom Hae Sang meets Ku San Young and he faces the demon which killed his mother.
Lee Hong Sae is a lieutenant in the violent crimes investigation team. He only cares about advancing his career in the police department. Due to Ku San Young and Yeom Hae Sang, he gets involved in mysterious cases.
(Source: AsianWiki)