Two people with the most unlucky fates can do nothing but send each other letters. 

Lay is an immortal who spends his days doing nothing but play the piano. Suho is a sickly patient who spends his days in the hospital.

One day, when a new piano arrives for Lay, he finds a letter attached to it by the wind. Out of curiousity, he mails to the address and thus begins the relationship built on letters but, what would a relationship between two such people be like? 

Lay and Suho both have never left the room they live in. Lay is there because he promised someone he would never leave and Suho is there because he was born with a special disease and was forced to grow up guarded and sheltered.