Guys, I just went reading back in chapter 1 and Gi Yoon said he saw ghost back in childhood so I think he and the ghost already met back in childhood or sm. So I think the ghost was trying to let Gi Yoon remember but Gi Yoon doesn't remember which leads the ghost to get angry. Gi Yoon also mentioned that he was bullied by someone who looks like Manager Jung Yi tae so I think the bully was the ghost or mayhe the Manager Jung Yi tae. (Who knows)