WHAT???

Grandpa or Taehee?

the grandpa ;-;

Well....
Spoiler...




Grandpa lost his son years ago so he suffered from trauma and mental breakdown for what happened to the son's soul. But, he is still an exorcist and has powers, so he knew that Taehee was the real deal. He took him as baby and was taking care of him until he "awakens" his powers or gets guided by the hometown (destiny). Once grandpa see the signs (blue fire and the breaking of the talismans) he knows that the agency will come to look for Taehee and kill him. So, while grandpa is still in a more passive mental state and he decides to sacrifice himself to help Taehee escape. He knows Taehee is the leader almost a god like person, or the hero they thought they got rid of 200 years ago. So grandpa gets rid of the spirits because he knew they would get on Taehee's way to escape (emotionally attached). He thought he was doing him a favor, but the truth is that this will mark Taehee forever. He will never forget grandpa and the spirits and all of this will only become regret and the heaviest emotional weight for Taehee.