Park Chanyeol comes from a prestigious family that owns the most renowed corporation: Park Industries. He's being groomed in becoming the heir to this corporation. He seems stuck up and snobby, but he has a good heart. Enter Byun Baekhyun, who has an extremely rare mental illness. It is called Cotard's syndrome or walking corpse syndrome. His parents don't know how to fully handle him, and kick him out onto the streets. Not caring whether he lives or dies. Which is where Chanyeol finds Baekhyun and forces him to live with him. 

Cotard's Syndrome- The Cotard delusion (also Cotard's Syndrome and Walking Corpse Syndrome) is a rare mental illness, in which the afflicted person holds the delusion that he or she is dead, either figuratively or literally; yet said delusion of negation is not a symptom essential to the syndrome proper. 

http://www.asianfanfics.com/story/view/1002625/delusion-of-the-mind-selfharm-hunhan-kaisoo-highschoolau-toaris-baekyeolangst