The one where the boy has a fatal disease and the doctor would do anything to save his life.  Kyungsoo is a home health care nurse. Jongin is a man with an incurable disease. 

Baekhyun gets left alone when Chen leaves for college. 

Red Thread of Fate;  According to a myth, the gods tie an invisible red cord around the ankles of those that are destined to meet one another in a certain situation or help each other in a certain way. Chanyeol would soon find out that anything was easier than tying a red string around Kyungsoo's cold heart, but that doesn't stop him from trying any chance he gets.