Park Chorong is quite but a sweet person. Not to anyone's knowledge, she is sick and keep it a secret except to her best friend. She never has the thought of finding love because of her condition.
 But then there is Yoon Bomi, being an easy going and straightforward girl she is, suddenly come into her life and stir her feeling after keep bugging her around telling “I love you, Unni”. Chorong want to give in but she is afraid that the person who might suffer in the end is Bomi herself.
Eventually the secret is revealed. Bomi insists to stay and make five promises to Chorong. Will she be able to keep those promises?

What are you doing here? You don't have to do this. I don't deserve you. I'm dying for God sake - Park Chorong

Unni, I'll do whatever it takes to keep those promises I’ve made to you. Have faith in me please - Yoon Bomi

Promises are the uniquely human way of ordering the future making it predictable and reliable to the extent that this is humanly possible ~ Hannah Arendt
However,
For every promise there is price to pay ~ Ji Rohn
So that is why

Only promise what you can deliver. Then deliver more than you promise ~ Anonymous