16 year old boy, A-Reum has Progeria Syndrome, a rare genetic defect that will cause the baby to show rapid aging from an early age. Although A-Reum has struggled again the disease, he was raised as a brilliant young child than anyone else. Young parents, Mira (SONG Hye-kyo) and Dae-su (KANG Dong-won) are still in their early 30s who had A-Ruem when they both were 17 year old, sometimes act immature but they never expressed their sorrow. A-Ruem only has few month to live, and Mira and Dae-su want to denied the reality. Although knowing that he does not have much time left, they appear on a fundraising TV show in hopes of raising enough money for his medical care. A-Ruem's appearance on a TV brings everyone's attention, and he becomes pen pal with a teenager girl who's also suffering from a disease watching the show. Exchanging letters with her becomes the joy of his days. But his body becomes more weary from aging, and he even loses his vision.