The Hanahaki Disease is an illness where the victim grows flowers in their lungs due to a one-sided love. Slowly the victim will start to throw up and cough up flower petals. If the love is not returned then the flowers will continue to grow until the victim is killed.  So what happens when one day Luhan coughs up a flower petal, knowing that he won't have long to live because the one he loves will never love him back.